diff --git a/tests/library/ConfigTest.php b/tests/library/ConfigTest.php
new file mode 100644
index 000000000..040582458
--- /dev/null
+++ b/tests/library/ConfigTest.php
@@ -0,0 +1,404 @@
+<?php
+
+use PHPUnit\Framework\TestCase;
+
+class ConfigTest extends TestCase
+{
+    private $config;
+    private $testConfigFile;
+    private $testConfigData;
+
+    protected function setUp(): void
+    {
+        $this->config = new Config();
+        $this->testConfigFile = sys_get_temp_dir() . '/test_config.ini';
+        $this->testConfigData = [
+            'database' => [
+                'host' => 'localhost',
+                'port' => 3306,
+                'username' => 'test_user',
+                'password' => 'test_pass',
+                'database' => 'test_db'
+            ],
+            'cache' => [
+                'enabled' => true,
+                'ttl' => 3600,
+                'driver' => 'redis'
+            ],
+            'app' => [
+                'name' => 'Test App',
+                'version' => '1.0.0',
+                'debug' => false
+            ]
+        ];
+    }
+
+    protected function tearDown(): void
+    {
+        if (file_exists($this->testConfigFile)) {
+            unlink($this->testConfigFile);
+        }
+    }
+
+    // Happy path tests
+    public function testConfigCanBeInstantiated()
+    {
+        $this->assertInstanceOf(Config::class, $this->config);
+    }
+
+    public function testSetAndGetConfigValue()
+    {
+        $this->config->set('test.key', 'test_value');
+        $this->assertEquals('test_value', $this->config->get('test.key'));
+    }
+
+    public function testSetAndGetNestedConfigValue()
+    {
+        $this->config->set('database.host', 'localhost');
+        $this->config->set('database.port', 3306);
+        
+        $this->assertEquals('localhost', $this->config->get('database.host'));
+        $this->assertEquals(3306, $this->config->get('database.port'));
+    }
+
+    public function testSetMultipleValuesAtOnce()
+    {
+        $this->config->setMultiple($this->testConfigData);
+        
+        $this->assertEquals('localhost', $this->config->get('database.host'));
+        $this->assertEquals(3306, $this->config->get('database.port'));
+        $this->assertEquals('test_user', $this->config->get('database.username'));
+        $this->assertTrue($this->config->get('cache.enabled'));
+        $this->assertEquals('Test App', $this->config->get('app.name'));
+    }
+
+    public function testHasConfigValue()
+    {
+        $this->config->set('test.key', 'value');
+        
+        $this->assertTrue($this->config->has('test.key'));
+        $this->assertFalse($this->config->has('nonexistent.key'));
+    }
+
+    public function testRemoveConfigValue()
+    {
+        $this->config->set('test.key', 'value');
+        $this->assertTrue($this->config->has('test.key'));
+        
+        $this->config->remove('test.key');
+        $this->assertFalse($this->config->has('test.key'));
+    }
+
+    public function testGetAllConfig()
+    {
+        $this->config->setMultiple($this->testConfigData);
+        $allConfig = $this->config->getAll();
+        
+        $this->assertIsArray($allConfig);
+        $this->assertArrayHasKey('database', $allConfig);
+        $this->assertArrayHasKey('cache', $allConfig);
+        $this->assertArrayHasKey('app', $allConfig);
+    }
+
+    public function testGetConfigSection()
+    {
+        $this->config->setMultiple($this->testConfigData);
+        $databaseConfig = $this->config->getSection('database');
+        
+        $this->assertIsArray($databaseConfig);
+        $this->assertEquals('localhost', $databaseConfig['host']);
+        $this->assertEquals(3306, $databaseConfig['port']);
+    }
+
+    // Edge cases and error conditions
+    public function testGetNonExistentConfigReturnsNull()
+    {
+        $this->assertNull($this->config->get('nonexistent.key'));
+    }
+
+    public function testGetNonExistentConfigReturnsDefaultValue()
+    {
+        $defaultValue = 'default_value';
+        $this->assertEquals($defaultValue, $this->config->get('nonexistent.key', $defaultValue));
+    }
+
+    public function testGetWithEmptyKey()
+    {
+        $this->assertNull($this->config->get(''));
+        $this->assertNull($this->config->get(null));
+    }
+
+    public function testSetWithEmptyKey()
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->config->set('', 'value');
+    }
+
+    public function testSetWithNullKey()
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->config->set(null, 'value');
+    }
+
+    public function testOverwriteExistingConfigValue()
+    {
+        $this->config->set('test.key', 'original_value');
+        $this->assertEquals('original_value', $this->config->get('test.key'));
+        
+        $this->config->set('test.key', 'new_value');
+        $this->assertEquals('new_value', $this->config->get('test.key'));
+    }
+
+    public function testSetComplexDataTypes()
+    {
+        $arrayValue = ['item1', 'item2', 'item3'];
+        $objectValue = new stdClass();
+        $objectValue->property = 'value';
+        
+        $this->config->set('test.array', $arrayValue);
+        $this->config->set('test.object', $objectValue);
+        
+        $this->assertEquals($arrayValue, $this->config->get('test.array'));
+        $this->assertEquals($objectValue, $this->config->get('test.object'));
+    }
+
+    public function testRemoveNonExistentKey()
+    {
+        // Should not throw an exception
+        $this->config->remove('nonexistent.key');
+        $this->assertFalse($this->config->has('nonexistent.key'));
+    }
+
+    public function testGetSectionNonExistent()
+    {
+        $result = $this->config->getSection('nonexistent');
+        $this->assertNull($result);
+    }
+
+    public function testClearAllConfig()
+    {
+        $this->config->setMultiple($this->testConfigData);
+        $this->assertTrue($this->config->has('database.host'));
+        
+        $this->config->clear();
+        $this->assertFalse($this->config->has('database.host'));
+        $this->assertEmpty($this->config->getAll());
+    }
+
+    // File operations tests
+    public function testLoadConfigFromFile()
+    {
+        $configContent = "[database]\nhost = localhost\nport = 3306\n\n[cache]\nenabled = true\nttl = 3600";
+        file_put_contents($this->testConfigFile, $configContent);
+        
+        $this->config->loadFromFile($this->testConfigFile);
+        
+        $this->assertEquals('localhost', $this->config->get('database.host'));
+        $this->assertEquals('3306', $this->config->get('database.port'));
+        $this->assertEquals('true', $this->config->get('cache.enabled'));
+        $this->assertEquals('3600', $this->config->get('cache.ttl'));
+    }
+
+    public function testLoadConfigFromNonExistentFile()
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->config->loadFromFile('/nonexistent/path/config.ini');
+    }
+
+    public function testSaveConfigToFile()
+    {
+        $this->config->setMultiple($this->testConfigData);
+        $this->config->saveToFile($this->testConfigFile);
+        
+        $this->assertFileExists($this->testConfigFile);
+        $content = file_get_contents($this->testConfigFile);
+        $this->assertStringContains('localhost', $content);
+        $this->assertStringContains('3306', $content);
+    }
+
+    public function testSaveConfigToInvalidPath()
+    {
+        $this->expectException(RuntimeException::class);
+        $this->config->saveToFile('/invalid/path/config.ini');
+    }
+
+    // Type casting and validation tests
+    public function testGetBooleanValue()
+    {
+        $this->config->set('test.bool_true', true);
+        $this->config->set('test.bool_false', false);
+        $this->config->set('test.bool_string_true', 'true');
+        $this->config->set('test.bool_string_false', 'false');
+        
+        $this->assertTrue($this->config->getBool('test.bool_true'));
+        $this->assertFalse($this->config->getBool('test.bool_false'));
+        $this->assertTrue($this->config->getBool('test.bool_string_true'));
+        $this->assertFalse($this->config->getBool('test.bool_string_false'));
+    }
+
+    public function testGetIntegerValue()
+    {
+        $this->config->set('test.int', 42);
+        $this->config->set('test.int_string', '123');
+        
+        $this->assertEquals(42, $this->config->getInt('test.int'));
+        $this->assertEquals(123, $this->config->getInt('test.int_string'));
+    }
+
+    public function testGetFloatValue()
+    {
+        $this->config->set('test.float', 3.14);
+        $this->config->set('test.float_string', '2.718');
+        
+        $this->assertEquals(3.14, $this->config->getFloat('test.float'));
+        $this->assertEquals(2.718, $this->config->getFloat('test.float_string'));
+    }
+
+    public function testGetArrayValue()
+    {
+        $arrayValue = ['a', 'b', 'c'];
+        $this->config->set('test.array', $arrayValue);
+        
+        $this->assertEquals($arrayValue, $this->config->getArray('test.array'));
+    }
+
+    // Environment variable integration tests
+    public function testGetFromEnvironmentVariable()
+    {
+        $_ENV['TEST_CONFIG_VALUE'] = 'env_value';
+        $this->config->set('test.env', '${TEST_CONFIG_VALUE}');
+        
+        $result = $this->config->get('test.env', null, true); // true for env expansion
+        $this->assertEquals('env_value', $result);
+        
+        unset($_ENV['TEST_CONFIG_VALUE']);
+    }
+
+    public function testGetFromEnvironmentVariableWithDefault()
+    {
+        $this->config->set('test.env', '${NONEXISTENT_VAR:default_value}');
+        
+        $result = $this->config->get('test.env', null, true);
+        $this->assertEquals('default_value', $result);
+    }
+
+    // Merge and extend functionality tests
+    public function testMergeConfigs()
+    {
+        $this->config->setMultiple([
+            'database' => ['host' => 'localhost', 'port' => 3306],
+            'cache' => ['enabled' => true]
+        ]);
+        
+        $additionalConfig = [
+            'database' => ['port' => 5432, 'ssl' => true],
+            'logging' => ['level' => 'debug']
+        ];
+        
+        $this->config->merge($additionalConfig);
+        
+        $this->assertEquals('localhost', $this->config->get('database.host'));
+        $this->assertEquals(5432, $this->config->get('database.port')); // Should be overwritten
+        $this->assertTrue($this->config->get('database.ssl')); // Should be added
+        $this->assertTrue($this->config->get('cache.enabled')); // Should remain
+        $this->assertEquals('debug', $this->config->get('logging.level')); // Should be added
+    }
+
+    // Performance and memory tests
+    public function testHandleLargeConfigData()
+    {
+        $largeData = [];
+        for ($i = 0; $i < 1000; $i++) {
+            $largeData["key_$i"] = "value_$i";
+        }
+        
+        $this->config->setMultiple(['large_section' => $largeData]);
+        
+        $this->assertEquals('value_500', $this->config->get('large_section.key_500'));
+        $this->assertEquals(1000, count($this->config->getSection('large_section')));
+    }
+
+    public function testConfigImmutability()
+    {
+        $originalData = ['immutable' => ['key' => 'value']];
+        $this->config->setMultiple($originalData);
+        
+        $retrievedData = $this->config->getSection('immutable');
+        $retrievedData['key'] = 'modified_value';
+        
+        // Original config should remain unchanged
+        $this->assertEquals('value', $this->config->get('immutable.key'));
+    }
+
+    // Validation and sanitization tests
+    public function testConfigKeyValidation()
+    {
+        $invalidKeys = ['', null, 123, [], new stdClass()];
+        
+        foreach ($invalidKeys as $key) {
+            try {
+                $this->config->set($key, 'value');
+                $this->fail('Expected InvalidArgumentException for invalid key: ' . var_export($key, true));
+            } catch (InvalidArgumentException $e) {
+                $this->assertTrue(true); // Expected exception
+            }
+        }
+    }
+
+    public function testNestedKeyDepthLimit()
+    {
+        // Test very deep nesting
+        $deepKey = implode('.', array_fill(0, 20, 'level'));
+        $this->config->set($deepKey, 'deep_value');
+        
+        $this->assertEquals('deep_value', $this->config->get($deepKey));
+    }
+
+    // Thread safety and concurrent access tests
+    public function testConcurrentAccess()
+    {
+        $this->config->set('concurrent.test', 'initial_value');
+        
+        // Simulate concurrent read/write operations
+        $processes = [];
+        for ($i = 0; $i < 5; $i++) {
+            $this->config->set("concurrent.key_$i", "value_$i");
+            $this->assertEquals("value_$i", $this->config->get("concurrent.key_$i"));
+        }
+        
+        $this->assertEquals('initial_value', $this->config->get('concurrent.test'));
+    }
+
+    // Serialization tests
+    public function testConfigSerialization()
+    {
+        $this->config->setMultiple($this->testConfigData);
+        
+        $serialized = serialize($this->config);
+        $unserialized = unserialize($serialized);
+        
+        $this->assertEquals($this->config->get('database.host'), $unserialized->get('database.host'));
+        $this->assertEquals($this->config->getAll(), $unserialized->getAll());
+    }
+
+    // Configuration validation tests
+    public function testRequiredConfigValidation()
+    {
+        $requiredKeys = ['database.host', 'database.port', 'app.name'];
+        
+        $this->config->setMultiple($this->testConfigData);
+        
+        foreach ($requiredKeys as $key) {
+            $this->assertTrue($this->config->has($key), "Required key '$key' is missing");
+        }
+    }
+
+    public function testConfigValueConstraints()
+    {
+        $this->config->set('database.port', 3306);
+        $port = $this->config->getInt('database.port');
+        
+        $this->assertGreaterThan(0, $port);
+        $this->assertLessThanOrEqual(65535, $port);
+    }
+}
\ No newline at end of file
diff --git a/tests/library/includes/PageHeaderTest.php b/tests/library/includes/PageHeaderTest.php
new file mode 100644
index 000000000..f3485981e
--- /dev/null
+++ b/tests/library/includes/PageHeaderTest.php
@@ -0,0 +1,548 @@
+<?php
+
+use PHPUnit\Framework\TestCase;
+use PHPUnit\Framework\MockObject\MockObject;
+
+/**
+ * Comprehensive unit tests for PageHeader class
+ * Testing Framework: PHPUnit
+ */
+class PageHeaderTest extends TestCase
+{
+    private $pageHeader;
+    private $mockRequest;
+    private $mockResponse;
+    private $mockConfig;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        
+        // Create mocks for dependencies
+        $this->mockRequest = $this->createMock(Request::class);
+        $this->mockResponse = $this->createMock(Response::class);
+        $this->mockConfig = $this->createMock(Config::class);
+        
+        // Initialize PageHeader with mocked dependencies
+        $this->pageHeader = new PageHeader($this->mockRequest, $this->mockResponse, $this->mockConfig);
+    }
+
+    protected function tearDown(): void
+    {
+        $this->pageHeader = null;
+        $this->mockRequest = null;
+        $this->mockResponse = null;
+        $this->mockConfig = null;
+        parent::tearDown();
+    }
+
+    /**
+     * Test basic header generation with default settings
+     */
+    public function testGenerateHeaderWithDefaults()
+    {
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['site_title', 'Test Site'],
+                ['site_description', 'Test Description'],
+                ['theme', 'default']
+            ]);
+
+        $header = $this->pageHeader->generateHeader();
+        
+        $this->assertNotEmpty($header);
+        $this->assertStringContainsString('Test Site', $header);
+        $this->assertStringContainsString('Test Description', $header);
+        $this->assertStringContainsString('<!DOCTYPE html>', $header);
+    }
+
+    /**
+     * Test header generation with custom title
+     */
+    public function testGenerateHeaderWithCustomTitle()
+    {
+        $customTitle = 'Custom Page Title';
+        
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['site_title', 'Test Site'],
+                ['site_description', 'Test Description'],
+                ['theme', 'default']
+            ]);
+
+        $header = $this->pageHeader->generateHeader($customTitle);
+        
+        $this->assertStringContainsString($customTitle, $header);
+        $this->assertStringContainsString('Test Site', $header);
+    }
+
+    /**
+     * Test header generation with empty title
+     */
+    public function testGenerateHeaderWithEmptyTitle()
+    {
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['site_title', 'Test Site'],
+                ['site_description', 'Test Description'],
+                ['theme', 'default']
+            ]);
+
+        $header = $this->pageHeader->generateHeader('');
+        
+        $this->assertStringContainsString('Test Site', $header);
+        $this->assertStringNotContainsString(' | ', $header);
+    }
+
+    /**
+     * Test header generation with null title
+     */
+    public function testGenerateHeaderWithNullTitle()
+    {
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['site_title', 'Test Site'],
+                ['site_description', 'Test Description'],
+                ['theme', 'default']
+            ]);
+
+        $header = $this->pageHeader->generateHeader(null);
+        
+        $this->assertStringContainsString('Test Site', $header);
+        $this->assertNotEmpty($header);
+    }
+
+    /**
+     * Test meta tag generation
+     */
+    public function testGenerateMetaTags()
+    {
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['site_description', 'Test Description'],
+                ['site_keywords', 'test,keywords,site'],
+                ['site_author', 'Test Author']
+            ]);
+
+        $metaTags = $this->pageHeader->generateMetaTags();
+        
+        $this->assertStringContainsString('name="description"', $metaTags);
+        $this->assertStringContainsString('Test Description', $metaTags);
+        $this->assertStringContainsString('name="keywords"', $metaTags);
+        $this->assertStringContainsString('test,keywords,site', $metaTags);
+        $this->assertStringContainsString('name="author"', $metaTags);
+        $this->assertStringContainsString('Test Author', $metaTags);
+    }
+
+    /**
+     * Test meta tag generation with missing configuration
+     */
+    public function testGenerateMetaTagsWithMissingConfig()
+    {
+        $this->mockConfig->method('get')
+            ->willReturn(null);
+
+        $metaTags = $this->pageHeader->generateMetaTags();
+        
+        $this->assertStringContainsString('name="viewport"', $metaTags);
+        $this->assertStringContainsString('charset=', $metaTags);
+    }
+
+    /**
+     * Test CSS link generation
+     */
+    public function testGenerateCssLinks()
+    {
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['theme', 'custom'],
+                ['css_files', ['main.css', 'theme.css']],
+                ['base_url', 'https://example.com']
+            ]);
+
+        $cssLinks = $this->pageHeader->generateCssLinks();
+        
+        $this->assertStringContainsString('rel="stylesheet"', $cssLinks);
+        $this->assertStringContainsString('main.css', $cssLinks);
+        $this->assertStringContainsString('theme.css', $cssLinks);
+        $this->assertStringContainsString('https://example.com', $cssLinks);
+    }
+
+    /**
+     * Test CSS link generation with empty CSS files
+     */
+    public function testGenerateCssLinksWithEmptyFiles()
+    {
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['theme', 'default'],
+                ['css_files', []],
+                ['base_url', 'https://example.com']
+            ]);
+
+        $cssLinks = $this->pageHeader->generateCssLinks();
+        
+        $this->assertStringContainsString('rel="stylesheet"', $cssLinks);
+        $this->assertStringContainsString('default', $cssLinks);
+    }
+
+    /**
+     * Test JavaScript link generation
+     */
+    public function testGenerateJsLinks()
+    {
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['js_files', ['main.js', 'utils.js']],
+                ['base_url', 'https://example.com']
+            ]);
+
+        $jsLinks = $this->pageHeader->generateJsLinks();
+        
+        $this->assertStringContainsString('src=', $jsLinks);
+        $this->assertStringContainsString('main.js', $jsLinks);
+        $this->assertStringContainsString('utils.js', $jsLinks);
+        $this->assertStringContainsString('https://example.com', $jsLinks);
+    }
+
+    /**
+     * Test JavaScript link generation with no JS files
+     */
+    public function testGenerateJsLinksWithNoFiles()
+    {
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['js_files', null],
+                ['base_url', 'https://example.com']
+            ]);
+
+        $jsLinks = $this->pageHeader->generateJsLinks();
+        
+        $this->assertEmpty($jsLinks);
+    }
+
+    /**
+     * Test canonical URL generation
+     */
+    public function testGenerateCanonicalUrl()
+    {
+        $this->mockRequest->method('getUri')
+            ->willReturn('https://example.com/page');
+        
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['canonical_url', true],
+                ['base_url', 'https://example.com']
+            ]);
+
+        $canonical = $this->pageHeader->generateCanonicalUrl();
+        
+        $this->assertStringContainsString('rel="canonical"', $canonical);
+        $this->assertStringContainsString('https://example.com/page', $canonical);
+    }
+
+    /**
+     * Test canonical URL generation when disabled
+     */
+    public function testGenerateCanonicalUrlWhenDisabled()
+    {
+        $this->mockConfig->method('get')
+            ->willReturn(false);
+
+        $canonical = $this->pageHeader->generateCanonicalUrl();
+        
+        $this->assertEmpty($canonical);
+    }
+
+    /**
+     * Test Open Graph meta tag generation
+     */
+    public function testGenerateOpenGraphTags()
+    {
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['og_title', 'Test OG Title'],
+                ['og_description', 'Test OG Description'],
+                ['og_image', 'https://example.com/image.jpg'],
+                ['og_url', 'https://example.com'],
+                ['og_type', 'website']
+            ]);
+
+        $ogTags = $this->pageHeader->generateOpenGraphTags();
+        
+        $this->assertStringContainsString('property="og:title"', $ogTags);
+        $this->assertStringContainsString('Test OG Title', $ogTags);
+        $this->assertStringContainsString('property="og:description"', $ogTags);
+        $this->assertStringContainsString('Test OG Description', $ogTags);
+        $this->assertStringContainsString('property="og:image"', $ogTags);
+        $this->assertStringContainsString('https://example.com/image.jpg', $ogTags);
+    }
+
+    /**
+     * Test Twitter Card meta tag generation
+     */
+    public function testGenerateTwitterCardTags()
+    {
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['twitter_card', 'summary'],
+                ['twitter_site', '@testsite'],
+                ['twitter_creator', '@testcreator'],
+                ['twitter_title', 'Test Twitter Title'],
+                ['twitter_description', 'Test Twitter Description'],
+                ['twitter_image', 'https://example.com/twitter-image.jpg']
+            ]);
+
+        $twitterTags = $this->pageHeader->generateTwitterCardTags();
+        
+        $this->assertStringContainsString('name="twitter:card"', $twitterTags);
+        $this->assertStringContainsString('summary', $twitterTags);
+        $this->assertStringContainsString('name="twitter:site"', $twitterTags);
+        $this->assertStringContainsString('@testsite', $twitterTags);
+        $this->assertStringContainsString('name="twitter:creator"', $twitterTags);
+        $this->assertStringContainsString('@testcreator', $twitterTags);
+    }
+
+    /**
+     * Test favicon generation
+     */
+    public function testGenerateFavicon()
+    {
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['favicon', 'favicon.ico'],
+                ['base_url', 'https://example.com']
+            ]);
+
+        $favicon = $this->pageHeader->generateFavicon();
+        
+        $this->assertStringContainsString('rel="icon"', $favicon);
+        $this->assertStringContainsString('favicon.ico', $favicon);
+        $this->assertStringContainsString('https://example.com', $favicon);
+    }
+
+    /**
+     * Test favicon generation with no favicon configured
+     */
+    public function testGenerateFaviconWithNone()
+    {
+        $this->mockConfig->method('get')
+            ->willReturn(null);
+
+        $favicon = $this->pageHeader->generateFavicon();
+        
+        $this->assertEmpty($favicon);
+    }
+
+    /**
+     * Test complete header generation with all components
+     */
+    public function testGenerateCompleteHeader()
+    {
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['site_title', 'Complete Test Site'],
+                ['site_description', 'Complete Test Description'],
+                ['theme', 'complete'],
+                ['css_files', ['main.css']],
+                ['js_files', ['main.js']],
+                ['canonical_url', true],
+                ['og_title', 'Test OG Title'],
+                ['twitter_card', 'summary'],
+                ['favicon', 'favicon.ico'],
+                ['base_url', 'https://example.com']
+            ]);
+
+        $this->mockRequest->method('getUri')
+            ->willReturn('https://example.com/complete');
+
+        $header = $this->pageHeader->generateCompleteHeader('Complete Page');
+        
+        $this->assertStringContainsString('<!DOCTYPE html>', $header);
+        $this->assertStringContainsString('Complete Page', $header);
+        $this->assertStringContainsString('Complete Test Site', $header);
+        $this->assertStringContainsString('rel="stylesheet"', $header);
+        $this->assertStringContainsString('main.css', $header);
+        $this->assertStringContainsString('main.js', $header);
+        $this->assertStringContainsString('rel="canonical"', $header);
+        $this->assertStringContainsString('property="og:title"', $header);
+        $this->assertStringContainsString('name="twitter:card"', $header);
+        $this->assertStringContainsString('rel="icon"', $header);
+    }
+
+    /**
+     * Test header generation with XSS protection
+     */
+    public function testGenerateHeaderWithXssProtection()
+    {
+        $maliciousTitle = '<script>alert("xss")</script>';
+        
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['site_title', 'Test Site'],
+                ['site_description', 'Test Description'],
+                ['theme', 'default']
+            ]);
+
+        $header = $this->pageHeader->generateHeader($maliciousTitle);
+        
+        $this->assertStringNotContainsString('<script>', $header);
+        $this->assertStringNotContainsString('alert("xss")', $header);
+        $this->assertStringContainsString('&lt;script&gt;', $header);
+    }
+
+    /**
+     * Test header generation with special characters
+     */
+    public function testGenerateHeaderWithSpecialCharacters()
+    {
+        $specialTitle = 'Café & Résumé - "Quotes" & \'Apostrophes\'';
+        
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['site_title', 'Test Site'],
+                ['site_description', 'Test Description'],
+                ['theme', 'default']
+            ]);
+
+        $header = $this->pageHeader->generateHeader($specialTitle);
+        
+        $this->assertStringContainsString($specialTitle, $header);
+        $this->assertStringContainsString('Test Site', $header);
+    }
+
+    /**
+     * Test header generation with very long title
+     */
+    public function testGenerateHeaderWithLongTitle()
+    {
+        $longTitle = str_repeat('Very Long Title ', 20);
+        
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['site_title', 'Test Site'],
+                ['site_description', 'Test Description'],
+                ['theme', 'default']
+            ]);
+
+        $header = $this->pageHeader->generateHeader($longTitle);
+        
+        $this->assertStringContainsString($longTitle, $header);
+        $this->assertNotEmpty($header);
+    }
+
+    /**
+     * Test error handling when config is unavailable
+     */
+    public function testGenerateHeaderWithUnavailableConfig()
+    {
+        $this->mockConfig->method('get')
+            ->willThrowException(new Exception('Config unavailable'));
+
+        $header = $this->pageHeader->generateHeader('Test Title');
+        
+        $this->assertStringContainsString('Test Title', $header);
+        $this->assertStringContainsString('<!DOCTYPE html>', $header);
+    }
+
+    /**
+     * Test header generation with RTL language support
+     */
+    public function testGenerateHeaderWithRtlLanguage()
+    {
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['site_title', 'موقع الاختبار'],
+                ['site_description', 'وصف الاختبار'],
+                ['language', 'ar'],
+                ['text_direction', 'rtl'],
+                ['theme', 'default']
+            ]);
+
+        $header = $this->pageHeader->generateHeader('صفحة الاختبار');
+        
+        $this->assertStringContainsString('dir="rtl"', $header);
+        $this->assertStringContainsString('lang="ar"', $header);
+        $this->assertStringContainsString('موقع الاختبار', $header);
+        $this->assertStringContainsString('صفحة الاختبار', $header);
+    }
+
+    /**
+     * Test header caching mechanism
+     */
+    public function testHeaderCaching()
+    {
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['site_title', 'Cached Site'],
+                ['site_description', 'Cached Description'],
+                ['theme', 'default'],
+                ['cache_headers', true]
+            ]);
+
+        $header1 = $this->pageHeader->generateHeader('Cached Page');
+        $header2 = $this->pageHeader->generateHeader('Cached Page');
+        
+        $this->assertEquals($header1, $header2);
+        $this->assertStringContainsString('Cached Page', $header1);
+        $this->assertStringContainsString('Cached Site', $header1);
+    }
+
+    /**
+     * Test responsive meta viewport tag
+     */
+    public function testResponsiveViewportTag()
+    {
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['responsive', true],
+                ['viewport_meta', 'width=device-width, initial-scale=1.0']
+            ]);
+
+        $metaTags = $this->pageHeader->generateMetaTags();
+        
+        $this->assertStringContainsString('name="viewport"', $metaTags);
+        $this->assertStringContainsString('width=device-width', $metaTags);
+        $this->assertStringContainsString('initial-scale=1.0', $metaTags);
+    }
+
+    /**
+     * Test CSP (Content Security Policy) header generation
+     */
+    public function testContentSecurityPolicyHeader()
+    {
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['csp_enabled', true],
+                ['csp_policy', "default-src 'self'; script-src 'self' 'unsafe-inline'"]
+            ]);
+
+        $cspHeader = $this->pageHeader->generateCspHeader();
+        
+        $this->assertStringContainsString('Content-Security-Policy', $cspHeader);
+        $this->assertStringContainsString("default-src 'self'", $cspHeader);
+        $this->assertStringContainsString("script-src 'self' 'unsafe-inline'", $cspHeader);
+    }
+
+    /**
+     * Test structured data (JSON-LD) generation
+     */
+    public function testStructuredDataGeneration()
+    {
+        $this->mockConfig->method('get')
+            ->willReturnMap([
+                ['structured_data', true],
+                ['site_name', 'Test Site'],
+                ['site_url', 'https://example.com'],
+                ['site_logo', 'https://example.com/logo.png']
+            ]);
+
+        $structuredData = $this->pageHeader->generateStructuredData();
+        
+        $this->assertStringContainsString('application/ld+json', $structuredData);
+        $this->assertStringContainsString('@context', $structuredData);
+        $this->assertStringContainsString('@type', $structuredData);
+        $this->assertStringContainsString('Test Site', $structuredData);
+        $this->assertStringContainsString('https://example.com', $structuredData);
+    }
+}
\ No newline at end of file
diff --git a/tests/templates/AdminIndexTemplateTest.php b/tests/templates/AdminIndexTemplateTest.php
new file mode 100644
index 000000000..70d4dbf38
--- /dev/null
+++ b/tests/templates/AdminIndexTemplateTest.php
@@ -0,0 +1,510 @@
+<?php
+
+use PHPUnit\Framework\TestCase;
+use PHPUnit\Framework\MockObject\MockObject;
+
+/**
+ * Comprehensive unit tests for AdminIndexTemplate
+ * 
+ * Tests cover happy paths, edge cases, and failure conditions
+ * Following PHPUnit best practices for clean, readable, and maintainable tests
+ */
+class AdminIndexTemplateTest extends TestCase
+{
+    private $adminIndexTemplate;
+    private $mockRequest;
+    private $mockResponse;
+    private $mockDatabase;
+    private $mockAuth;
+
+    /**
+     * Set up test fixtures before each test
+     */
+    protected function setUp(): void
+    {
+        parent::setUp();
+        
+        // Create mock dependencies
+        $this->mockRequest = $this->createMock(Request::class);
+        $this->mockResponse = $this->createMock(Response::class);
+        $this->mockDatabase = $this->createMock(Database::class);
+        $this->mockAuth = $this->createMock(Auth::class);
+        
+        // Initialize the template with mocked dependencies
+        $this->adminIndexTemplate = new AdminIndexTemplate(
+            $this->mockRequest,
+            $this->mockResponse,
+            $this->mockDatabase,
+            $this->mockAuth
+        );
+    }
+
+    /**
+     * Clean up after each test
+     */
+    protected function tearDown(): void
+    {
+        $this->adminIndexTemplate = null;
+        parent::tearDown();
+    }
+
+    /**
+     * Test successful template rendering with valid admin user
+     */
+    public function testRenderWithValidAdminUser(): void
+    {
+        // Arrange
+        $mockUser = $this->createMockUser('admin', ['admin' => true]);
+        $this->mockAuth->expects($this->once())
+            ->method('getCurrentUser')
+            ->willReturn($mockUser);
+        
+        $this->mockDatabase->expects($this->once())
+            ->method('getAdminStats')
+            ->willReturn([
+                'total_users' => 100,
+                'active_sessions' => 15,
+                'pending_reviews' => 5
+            ]);
+
+        // Act
+        $result = $this->adminIndexTemplate->render();
+
+        // Assert
+        $this->assertIsString($result);
+        $this->assertStringContainsString('Admin Dashboard', $result);
+        $this->assertStringContainsString('100', $result); // total users
+        $this->assertStringContainsString('15', $result);  // active sessions
+        $this->assertStringContainsString('5', $result);   // pending reviews
+    }
+
+    /**
+     * Test template rendering fails with unauthorized user
+     */
+    public function testRenderWithUnauthorizedUser(): void
+    {
+        // Arrange
+        $mockUser = $this->createMockUser('user', ['admin' => false]);
+        $this->mockAuth->expects($this->once())
+            ->method('getCurrentUser')
+            ->willReturn($mockUser);
+
+        // Act & Assert
+        $this->expectException(UnauthorizedException::class);
+        $this->expectExceptionMessage('Access denied: Admin privileges required');
+        
+        $this->adminIndexTemplate->render();
+    }
+
+    /**
+     * Test template rendering with null/guest user
+     */
+    public function testRenderWithNullUser(): void
+    {
+        // Arrange
+        $this->mockAuth->expects($this->once())
+            ->method('getCurrentUser')
+            ->willReturn(null);
+
+        // Act & Assert
+        $this->expectException(UnauthorizedException::class);
+        $this->expectExceptionMessage('Access denied: Authentication required');
+        
+        $this->adminIndexTemplate->render();
+    }
+
+    /**
+     * Test template rendering with database connection failure
+     */
+    public function testRenderWithDatabaseFailure(): void
+    {
+        // Arrange
+        $mockUser = $this->createMockUser('admin', ['admin' => true]);
+        $this->mockAuth->expects($this->once())
+            ->method('getCurrentUser')
+            ->willReturn($mockUser);
+        
+        $this->mockDatabase->expects($this->once())
+            ->method('getAdminStats')
+            ->willThrowException(new DatabaseException('Connection failed'));
+
+        // Act & Assert
+        $this->expectException(DatabaseException::class);
+        $this->expectExceptionMessage('Connection failed');
+        
+        $this->adminIndexTemplate->render();
+    }
+
+    /**
+     * Test template rendering with empty/invalid database response
+     */
+    public function testRenderWithEmptyDatabaseResponse(): void
+    {
+        // Arrange
+        $mockUser = $this->createMockUser('admin', ['admin' => true]);
+        $this->mockAuth->expects($this->once())
+            ->method('getCurrentUser')
+            ->willReturn($mockUser);
+        
+        $this->mockDatabase->expects($this->once())
+            ->method('getAdminStats')
+            ->willReturn([]);
+
+        // Act
+        $result = $this->adminIndexTemplate->render();
+
+        // Assert
+        $this->assertIsString($result);
+        $this->assertStringContainsString('Admin Dashboard', $result);
+        $this->assertStringContainsString('0', $result); // Should show zero for missing stats
+    }
+
+    /**
+     * Test template rendering with malformed database response
+     */
+    public function testRenderWithMalformedDatabaseResponse(): void
+    {
+        // Arrange
+        $mockUser = $this->createMockUser('admin', ['admin' => true]);
+        $this->mockAuth->expects($this->once())
+            ->method('getCurrentUser')
+            ->willReturn($mockUser);
+        
+        $this->mockDatabase->expects($this->once())
+            ->method('getAdminStats')
+            ->willReturn(['invalid' => 'data']);
+
+        // Act
+        $result = $this->adminIndexTemplate->render();
+
+        // Assert
+        $this->assertIsString($result);
+        $this->assertStringContainsString('Admin Dashboard', $result);
+        // Should gracefully handle missing expected keys
+    }
+
+    /**
+     * Test template CSS and JavaScript inclusion
+     */
+    public function testRenderIncludesAssets(): void
+    {
+        // Arrange
+        $mockUser = $this->createMockUser('admin', ['admin' => true]);
+        $this->mockAuth->expects($this->once())
+            ->method('getCurrentUser')
+            ->willReturn($mockUser);
+        
+        $this->mockDatabase->expects($this->once())
+            ->method('getAdminStats')
+            ->willReturn(['total_users' => 50]);
+
+        // Act
+        $result = $this->adminIndexTemplate->render();
+
+        // Assert
+        $this->assertStringContainsString('<link', $result);
+        $this->assertStringContainsString('admin.css', $result);
+        $this->assertStringContainsString('<script', $result);
+        $this->assertStringContainsString('admin.js', $result);
+    }
+
+    /**
+     * Test template meta tags and title
+     */
+    public function testRenderIncludesMetaTags(): void
+    {
+        // Arrange
+        $mockUser = $this->createMockUser('admin', ['admin' => true]);
+        $this->mockAuth->expects($this->once())
+            ->method('getCurrentUser')
+            ->willReturn($mockUser);
+        
+        $this->mockDatabase->expects($this->once())
+            ->method('getAdminStats')
+            ->willReturn(['total_users' => 25]);
+
+        // Act
+        $result = $this->adminIndexTemplate->render();
+
+        // Assert
+        $this->assertStringContainsString('<title>Admin Dashboard</title>', $result);
+        $this->assertStringContainsString('<meta charset="utf-8">', $result);
+        $this->assertStringContainsString('<meta name="viewport"', $result);
+        $this->assertStringContainsString('content="width=device-width"', $result);
+    }
+
+    /**
+     * Test template navigation elements
+     */
+    public function testRenderIncludesNavigation(): void
+    {
+        // Arrange
+        $mockUser = $this->createMockUser('admin', ['admin' => true]);
+        $this->mockAuth->expects($this->once())
+            ->method('getCurrentUser')
+            ->willReturn($mockUser);
+        
+        $this->mockDatabase->expects($this->once())
+            ->method('getAdminStats')
+            ->willReturn(['total_users' => 75]);
+
+        // Act
+        $result = $this->adminIndexTemplate->render();
+
+        // Assert
+        $this->assertStringContainsString('<nav', $result);
+        $this->assertStringContainsString('Users', $result);
+        $this->assertStringContainsString('Settings', $result);
+        $this->assertStringContainsString('Reports', $result);
+        $this->assertStringContainsString('Logout', $result);
+    }
+
+    /**
+     * Test template with extremely large database values
+     */
+    public function testRenderWithLargeStatValues(): void
+    {
+        // Arrange
+        $mockUser = $this->createMockUser('admin', ['admin' => true]);
+        $this->mockAuth->expects($this->once())
+            ->method('getCurrentUser')
+            ->willReturn($mockUser);
+        
+        $this->mockDatabase->expects($this->once())
+            ->method('getAdminStats')
+            ->willReturn([
+                'total_users' => 999999999,
+                'active_sessions' => 50000,
+                'pending_reviews' => 10000
+            ]);
+
+        // Act
+        $result = $this->adminIndexTemplate->render();
+
+        // Assert
+        $this->assertIsString($result);
+        $this->assertStringContainsString('999,999,999', $result); // Should format large numbers
+    }
+
+    /**
+     * Test template with negative database values
+     */
+    public function testRenderWithNegativeStatValues(): void
+    {
+        // Arrange
+        $mockUser = $this->createMockUser('admin', ['admin' => true]);
+        $this->mockAuth->expects($this->once())
+            ->method('getCurrentUser')
+            ->willReturn($mockUser);
+        
+        $this->mockDatabase->expects($this->once())
+            ->method('getAdminStats')
+            ->willReturn([
+                'total_users' => -5,
+                'active_sessions' => -1,
+                'pending_reviews' => -10
+            ]);
+
+        // Act
+        $result = $this->adminIndexTemplate->render();
+
+        // Assert
+        $this->assertIsString($result);
+        // Should handle negative values gracefully, possibly converting to 0
+        $this->assertStringNotContainsString('-5', $result);
+    }
+
+    /**
+     * Test template XSS prevention
+     */
+    public function testRenderPreventsXSS(): void
+    {
+        // Arrange
+        $mockUser = $this->createMockUser('admin<script>alert("xss")</script>', ['admin' => true]);
+        $this->mockAuth->expects($this->once())
+            ->method('getCurrentUser')
+            ->willReturn($mockUser);
+        
+        $this->mockDatabase->expects($this->once())
+            ->method('getAdminStats')
+            ->willReturn(['total_users' => 100]);
+
+        // Act
+        $result = $this->adminIndexTemplate->render();
+
+        // Assert
+        $this->assertIsString($result);
+        $this->assertStringNotContainsString('<script>alert("xss")</script>', $result);
+        $this->assertStringContainsString('&lt;script&gt;', $result); // Should be escaped
+    }
+
+    /**
+     * Test template caching functionality
+     */
+    public function testRenderWithCaching(): void
+    {
+        // Arrange
+        $mockUser = $this->createMockUser('admin', ['admin' => true]);
+        $this->mockAuth->expects($this->exactly(2))
+            ->method('getCurrentUser')
+            ->willReturn($mockUser);
+        
+        $this->mockDatabase->expects($this->once()) // Should only call once due to caching
+            ->method('getAdminStats')
+            ->willReturn(['total_users' => 100]);
+
+        // Act
+        $result1 = $this->adminIndexTemplate->render();
+        $result2 = $this->adminIndexTemplate->render();
+
+        // Assert
+        $this->assertEquals($result1, $result2);
+    }
+
+    /**
+     * Test template rendering with custom theme
+     */
+    public function testRenderWithCustomTheme(): void
+    {
+        // Arrange
+        $mockUser = $this->createMockUser('admin', ['admin' => true, 'theme' => 'dark']);
+        $this->mockAuth->expects($this->once())
+            ->method('getCurrentUser')
+            ->willReturn($mockUser);
+        
+        $this->mockDatabase->expects($this->once())
+            ->method('getAdminStats')
+            ->willReturn(['total_users' => 100]);
+
+        // Act
+        $result = $this->adminIndexTemplate->render();
+
+        // Assert
+        $this->assertStringContainsString('theme-dark', $result);
+    }
+
+    /**
+     * Test template accessibility features
+     */
+    public function testRenderIncludesAccessibilityFeatures(): void
+    {
+        // Arrange
+        $mockUser = $this->createMockUser('admin', ['admin' => true]);
+        $this->mockAuth->expects($this->once())
+            ->method('getCurrentUser')
+            ->willReturn($mockUser);
+        
+        $this->mockDatabase->expects($this->once())
+            ->method('getAdminStats')
+            ->willReturn(['total_users' => 100]);
+
+        // Act
+        $result = $this->adminIndexTemplate->render();
+
+        // Assert
+        $this->assertStringContainsString('aria-label', $result);
+        $this->assertStringContainsString('role=', $result);
+        $this->assertStringContainsString('alt=', $result);
+    }
+
+    /**
+     * Helper method to create mock user objects
+     */
+    private function createMockUser(string $username, array $attributes = []): MockObject
+    {
+        $mockUser = $this->createMock(User::class);
+        
+        $mockUser->expects($this->any())
+            ->method('getUsername')
+            ->willReturn($username);
+            
+        $mockUser->expects($this->any())
+            ->method('hasRole')
+            ->with('admin')
+            ->willReturn($attributes['admin'] ?? false);
+            
+        $mockUser->expects($this->any())
+            ->method('getTheme')
+            ->willReturn($attributes['theme'] ?? 'default');
+            
+        return $mockUser;
+    }
+
+    /**
+     * Test template rendering performance with large datasets
+     */
+    public function testRenderPerformanceWithLargeDataset(): void
+    {
+        // Arrange
+        $mockUser = $this->createMockUser('admin', ['admin' => true]);
+        $this->mockAuth->expects($this->once())
+            ->method('getCurrentUser')
+            ->willReturn($mockUser);
+        
+        $this->mockDatabase->expects($this->once())
+            ->method('getAdminStats')
+            ->willReturn(['total_users' => 1000000]);
+
+        // Act
+        $startTime = microtime(true);
+        $result = $this->adminIndexTemplate->render();
+        $endTime = microtime(true);
+
+        // Assert
+        $this->assertIsString($result);
+        $this->assertLessThan(1.0, $endTime - $startTime); // Should render in under 1 second
+    }
+
+    /**
+     * Test template error handling with invalid template file
+     */
+    public function testRenderWithMissingTemplateFile(): void
+    {
+        // Arrange
+        $adminIndexTemplate = new AdminIndexTemplate(
+            $this->mockRequest,
+            $this->mockResponse,
+            $this->mockDatabase,
+            $this->mockAuth,
+            '/nonexistent/template.php' // Invalid template path
+        );
+        
+        $mockUser = $this->createMockUser('admin', ['admin' => true]);
+        $this->mockAuth->expects($this->once())
+            ->method('getCurrentUser')
+            ->willReturn($mockUser);
+
+        // Act & Assert
+        $this->expectException(TemplateNotFoundException::class);
+        $adminIndexTemplate->render();
+    }
+
+    /**
+     * Test template rendering with concurrent access
+     */
+    public function testRenderWithConcurrentAccess(): void
+    {
+        // Arrange
+        $mockUser = $this->createMockUser('admin', ['admin' => true]);
+        $this->mockAuth->expects($this->exactly(3))
+            ->method('getCurrentUser')
+            ->willReturn($mockUser);
+        
+        $this->mockDatabase->expects($this->exactly(3))
+            ->method('getAdminStats')
+            ->willReturn(['total_users' => 100]);
+
+        // Act - Simulate concurrent rendering
+        $results = [];
+        for ($i = 0; $i < 3; $i++) {
+            $results[] = $this->adminIndexTemplate->render();
+        }
+
+        // Assert
+        $this->assertCount(3, $results);
+        foreach ($results as $result) {
+            $this->assertIsString($result);
+            $this->assertStringContainsString('Admin Dashboard', $result);
+        }
+    }
+}
\ No newline at end of file
diff --git a/tests/templates/DefaultPageHeaderTemplateTest.php b/tests/templates/DefaultPageHeaderTemplateTest.php
new file mode 100644
index 000000000..037c67ee0
--- /dev/null
+++ b/tests/templates/DefaultPageHeaderTemplateTest.php
@@ -0,0 +1,465 @@
+<?php
+
+namespace Tests\Templates;
+
+use PHPUnit\Framework\TestCase;
+use PHPUnit\Framework\MockObject\MockObject;
+use App\Templates\DefaultPageHeaderTemplate;
+use App\Models\Page;
+use App\Models\User;
+use App\Services\NavigationService;
+use App\Services\ThemeService;
+use App\Exceptions\TemplateException;
+
+class DefaultPageHeaderTemplateTest extends TestCase
+{
+    private DefaultPageHeaderTemplate $template;
+    private MockObject $navigationService;
+    private MockObject $themeService;
+    private MockObject $page;
+    private MockObject $user;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+        
+        $this->navigationService = $this->createMock(NavigationService::class);
+        $this->themeService = $this->createMock(ThemeService::class);
+        $this->page = $this->createMock(Page::class);
+        $this->user = $this->createMock(User::class);
+        
+        $this->template = new DefaultPageHeaderTemplate(
+            $this->navigationService,
+            $this->themeService
+        );
+    }
+
+    protected function tearDown(): void
+    {
+        parent::tearDown();
+        unset($this->template, $this->navigationService, $this->themeService, $this->page, $this->user);
+    }
+
+    /**
+     * @test
+     */
+    public function it_renders_basic_header_with_page_title(): void
+    {
+        $this->page->method('getTitle')->willReturn('Test Page');
+        $this->page->method('getMetaDescription')->willReturn('Test description');
+        $this->themeService->method('getCurrentTheme')->willReturn('default');
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('<title>Test Page</title>', $result);
+        $this->assertStringContainsString('<meta name="description" content="Test description">', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_renders_header_with_user_authentication(): void
+    {
+        $this->page->method('getTitle')->willReturn('Dashboard');
+        $this->user->method('getName')->willReturn('John Doe');
+        $this->user->method('getEmail')->willReturn('john@example.com');
+        $this->user->method('isAuthenticated')->willReturn(true);
+        
+        $result = $this->template->render($this->page, $this->user);
+        
+        $this->assertStringContainsString('John Doe', $result);
+        $this->assertStringContainsString('john@example.com', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_renders_header_for_anonymous_user(): void
+    {
+        $this->page->method('getTitle')->willReturn('Public Page');
+        $this->user->method('isAuthenticated')->willReturn(false);
+        
+        $result = $this->template->render($this->page, $this->user);
+        
+        $this->assertStringContainsString('Login', $result);
+        $this->assertStringContainsString('Register', $result);
+        $this->assertStringNotContainsString('Logout', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_includes_navigation_menu(): void
+    {
+        $this->page->method('getTitle')->willReturn('Test Page');
+        $this->navigationService->method('getMainMenu')->willReturn([
+            ['label' => 'Home', 'url' => '/'],
+            ['label' => 'About', 'url' => '/about'],
+            ['label' => 'Contact', 'url' => '/contact']
+        ]);
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('Home', $result);
+        $this->assertStringContainsString('About', $result);
+        $this->assertStringContainsString('Contact', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_applies_theme_specific_styling(): void
+    {
+        $this->page->method('getTitle')->willReturn('Themed Page');
+        $this->themeService->method('getCurrentTheme')->willReturn('dark');
+        $this->themeService->method('getThemeStyles')->willReturn([
+            'header-bg' => '#333333',
+            'header-text' => '#ffffff'
+        ]);
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('#333333', $result);
+        $this->assertStringContainsString('#ffffff', $result);
+        $this->assertStringContainsString('theme-dark', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_handles_empty_page_title(): void
+    {
+        $this->page->method('getTitle')->willReturn('');
+        $this->page->method('getSlug')->willReturn('test-page');
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('<title>Untitled Page</title>', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_handles_null_page_title(): void
+    {
+        $this->page->method('getTitle')->willReturn(null);
+        $this->page->method('getSlug')->willReturn('test-page');
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('<title>Untitled Page</title>', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_sanitizes_page_title_for_xss(): void
+    {
+        $this->page->method('getTitle')->willReturn('<script>alert("xss")</script>');
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringNotContainsString('<script>', $result);
+        $this->assertStringContainsString('&lt;script&gt;', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_includes_canonical_url(): void
+    {
+        $this->page->method('getTitle')->willReturn('Test Page');
+        $this->page->method('getCanonicalUrl')->willReturn('https://example.com/test-page');
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('<link rel="canonical" href="https://example.com/test-page">', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_includes_open_graph_meta_tags(): void
+    {
+        $this->page->method('getTitle')->willReturn('Test Page');
+        $this->page->method('getMetaDescription')->willReturn('Test description');
+        $this->page->method('getOpenGraphImage')->willReturn('https://example.com/image.jpg');
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('<meta property="og:title" content="Test Page">', $result);
+        $this->assertStringContainsString('<meta property="og:description" content="Test description">', $result);
+        $this->assertStringContainsString('<meta property="og:image" content="https://example.com/image.jpg">', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_includes_twitter_meta_tags(): void
+    {
+        $this->page->method('getTitle')->willReturn('Test Page');
+        $this->page->method('getMetaDescription')->willReturn('Test description');
+        $this->page->method('getTwitterImage')->willReturn('https://example.com/twitter-image.jpg');
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('<meta name="twitter:title" content="Test Page">', $result);
+        $this->assertStringContainsString('<meta name="twitter:description" content="Test description">', $result);
+        $this->assertStringContainsString('<meta name="twitter:image" content="https://example.com/twitter-image.jpg">', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_handles_long_page_titles(): void
+    {
+        $longTitle = str_repeat('Very Long Title ', 20);
+        $this->page->method('getTitle')->willReturn($longTitle);
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('<title>', $result);
+        $this->assertLessThan(70, strlen($this->extractTitleFromHtml($result)));
+    }
+
+    /**
+     * @test
+     */
+    public function it_includes_responsive_meta_viewport(): void
+    {
+        $this->page->method('getTitle')->willReturn('Test Page');
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('<meta name="viewport" content="width=device-width, initial-scale=1">', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_includes_charset_meta_tag(): void
+    {
+        $this->page->method('getTitle')->willReturn('Test Page');
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('<meta charset="UTF-8">', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_handles_special_characters_in_title(): void
+    {
+        $this->page->method('getTitle')->willReturn('Test & Page "with" quotes');
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('Test &amp; Page &quot;with&quot; quotes', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_includes_breadcrumb_navigation(): void
+    {
+        $this->page->method('getTitle')->willReturn('Test Page');
+        $this->navigationService->method('getBreadcrumbs')->willReturn([
+            ['label' => 'Home', 'url' => '/'],
+            ['label' => 'Category', 'url' => '/category'],
+            ['label' => 'Test Page', 'url' => '/category/test-page']
+        ]);
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('breadcrumb', $result);
+        $this->assertStringContainsString('Home', $result);
+        $this->assertStringContainsString('Category', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_throws_exception_when_page_is_null(): void
+    {
+        $this->expectException(TemplateException::class);
+        $this->expectExceptionMessage('Page cannot be null');
+        
+        $this->template->render(null);
+    }
+
+    /**
+     * @test
+     */
+    public function it_handles_navigation_service_failure(): void
+    {
+        $this->page->method('getTitle')->willReturn('Test Page');
+        $this->navigationService->method('getMainMenu')->willThrowException(new \Exception('Navigation service unavailable'));
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('<title>Test Page</title>', $result);
+        $this->assertStringNotContainsString('Navigation service unavailable', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_handles_theme_service_failure(): void
+    {
+        $this->page->method('getTitle')->willReturn('Test Page');
+        $this->themeService->method('getCurrentTheme')->willThrowException(new \Exception('Theme service unavailable'));
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('<title>Test Page</title>', $result);
+        $this->assertStringContainsString('theme-default', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_includes_csrf_token_in_forms(): void
+    {
+        $this->page->method('getTitle')->willReturn('Test Page');
+        $this->user->method('isAuthenticated')->willReturn(true);
+        
+        $result = $this->template->render($this->page, $this->user);
+        
+        $this->assertStringContainsString('csrf_token', $result);
+        $this->assertStringContainsString('name="_token"', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_includes_language_attributes(): void
+    {
+        $this->page->method('getTitle')->willReturn('Test Page');
+        $this->page->method('getLanguage')->willReturn('en');
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('lang="en"', $result);
+        $this->assertStringContainsString('hreflang="en"', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_includes_search_functionality(): void
+    {
+        $this->page->method('getTitle')->willReturn('Test Page');
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('search', $result);
+        $this->assertStringContainsString('type="search"', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_handles_mobile_specific_rendering(): void
+    {
+        $_SERVER['HTTP_USER_AGENT'] = 'Mozilla/5.0 (iPhone; CPU iPhone OS 14_0 like Mac OS X) AppleWebKit/605.1.15';
+        
+        $this->page->method('getTitle')->willReturn('Test Page');
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('mobile-header', $result);
+        $this->assertStringContainsString('hamburger-menu', $result);
+        
+        unset($_SERVER['HTTP_USER_AGENT']);
+    }
+
+    /**
+     * @test
+     */
+    public function it_renders_with_custom_css_classes(): void
+    {
+        $this->page->method('getTitle')->willReturn('Test Page');
+        $this->page->method('getCssClasses')->willReturn(['custom-class', 'another-class']);
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('custom-class', $result);
+        $this->assertStringContainsString('another-class', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_includes_accessibility_attributes(): void
+    {
+        $this->page->method('getTitle')->willReturn('Test Page');
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('role="banner"', $result);
+        $this->assertStringContainsString('aria-label', $result);
+        $this->assertStringContainsString('skip-to-content', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_performance_with_large_navigation_menu(): void
+    {
+        $this->page->method('getTitle')->willReturn('Test Page');
+        
+        $largeMenu = [];
+        for ($i = 1; $i <= 100; $i++) {
+            $largeMenu[] = ['label' => "Item $i", 'url' => "/item-$i"];
+        }
+        $this->navigationService->method('getMainMenu')->willReturn($largeMenu);
+        
+        $startTime = microtime(true);
+        $result = $this->template->render($this->page);
+        $endTime = microtime(true);
+        
+        $this->assertLessThan(0.1, $endTime - $startTime, 'Template rendering should be fast even with large menus');
+        $this->assertStringContainsString('Item 1', $result);
+        $this->assertStringContainsString('Item 100', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_handles_unicode_characters_in_title(): void
+    {
+        $this->page->method('getTitle')->willReturn('Test Page with émojis 🚀 and unicode ñ');
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('émojis 🚀 and unicode ñ', $result);
+    }
+
+    /**
+     * @test
+     */
+    public function it_generates_valid_html5_markup(): void
+    {
+        $this->page->method('getTitle')->willReturn('Test Page');
+        
+        $result = $this->template->render($this->page);
+        
+        $this->assertStringContainsString('<!DOCTYPE html>', $result);
+        $this->assertStringContainsString('<html', $result);
+        $this->assertStringContainsString('<head>', $result);
+        $this->assertStringContainsString('</head>', $result);
+        $this->assertStringContainsString('<body', $result);
+    }
+
+    /**
+     * Helper method to extract title from HTML string
+     */
+    private function extractTitleFromHtml(string $html): string
+    {
+        if (preg_match('/<title>(.*?)<\/title>/', $html, $matches)) {
+            return $matches[1];
+        }
+        return '';
+    }
+}
\ No newline at end of file