Add initial test for net_linux.go

More tests needed based on iwlist output, but the side-effect-free
part of GetSupportedFrequencies() has been been broken out into a function
that can now be tested without calling core.Exec().

network/net_linux_test.go

@@ -0,0 +1,40 @@
+package network
+
+import (
+	"errors"
+	"reflect"
+	"testing"
+)
+
+func TestProcessSupportedFrequencies(t *testing.T) {
+	// Actually test processSupportedFrequencies; IO is lifted out.
+	cases := []struct {
+		Name          string
+		InputString   string
+		InputError    error
+		ExpectedFreqs []int
+		ExpectedError bool
+	}{
+		{
+			"Returns empty with an error",
+			"Shouldn't matter",
+			errors.New("iwlist must have failed"),
+			[]int{},
+			true,
+		},
+	}
+	for _, test := range cases {
+		t.Run(test.Name, func(t *testing.T) {
+			freqs, err := processSupportedFrequencies(test.InputString, test.InputError)
+			if err != nil && !test.ExpectedError {
+				t.Errorf("unexpected error: %s", err)
+			}
+			if err == nil && test.ExpectedError {
+				t.Error("expected error, but got none")
+			}
+			if !test.ExpectedError && !reflect.DeepEqual(freqs, test.ExpectedFreqs) {
+				t.Errorf("got %v, want %v", freqs, test.ExpectedFreqs)
+			}
+		})
+	}
+}