Add tests for settings code

settings.go

@@ -17,7 +17,7 @@ type settings struct {
 	changeListeners []chan Settings
 }
 
-var singleton *settings
+var settingsCache *settings
 
 func (s *settings) Theme() string {
 	return s.theme
@@ -55,9 +55,9 @@ func loadSettings() *settings {
 
 // GetSettings returns the system wide settings currently configured
 func GetSettings() Settings {
-	if singleton == nil {
-		singleton = loadSettings()
+	if settingsCache == nil {
+		settingsCache = loadSettings()
 	}
 
-	return singleton
+	return settingsCache
 }

settings_test.go

@@ -0,0 +1,38 @@
+package fyne
+
+import "os"
+import "time"
+
+import "testing"
+import "github.com/stretchr/testify/assert"
+
+func TestThemeDefault(t *testing.T) {
+	assert.Equal(t, "dark", GetSettings().Theme())
+}
+
+func TestThemeFromEnv(t *testing.T) {
+	settingsCache = nil
+	os.Setenv("FYNE_THEME", "light")
+
+	assert.Equal(t, "light", GetSettings().Theme())
+}
+
+func TestSetTheme(t *testing.T) {
+	GetSettings().SetTheme("light")
+
+	assert.Equal(t, "light", GetSettings().Theme())
+}
+
+func TestListenerCallback(t *testing.T) {
+	listener := make(chan Settings)
+	GetSettings().AddChangeListener(listener)
+	GetSettings().SetTheme("light")
+
+	func() {
+		select {
+		case <-listener:
+		case <-time.After(1 * time.Second):
+			assert.Fail(t, "Timed out waiting for callback")
+		}
+	}()
+}