fix tests for exercism.paths on systems with $XDG_CONFIG_HOME

In case `$XDG_CONFIG_HOME` is set, tests of paths package fail as
config home was not mocked properly.

The patch simplifies paths' internals and introduces a more flexible
way to mock globals of `paths` package.

Author: Vladimir Varankin

config/config_test.go

@@ -26,6 +26,7 @@ func TestLoad(t *testing.T) {
 		t.Fatal(err)
 	}
 	paths.Home = tmpDir
+	paths.ConfigHome = tmpDir
 
 	testCases := []struct {
 		desc                string

paths/paths.go

@@ -20,15 +20,20 @@ const (
 var (
 	// Home by default will contact the location of your home directory.
 	Home string
+	// ConfigHome will contain $XDG_CONFIG_HOME if it exists or Home otherwise.
+	ConfigHome string
 
-	// XDGConfigHome will contain $XDG_CONFIG_HOME if it exists.
-	XDGConfigHome   string
 	errHomeNotFound = errors.New("unable to locate home directory")
 )
 
 func init() {
+	home, err := findHome()
+	if err != nil {
+		panic(err)
+	}
+	configHome := os.Getenv("XDG_CONFIG_HOME")
 	// on startup set default values
-	Recalculate()
+	Recalculate(home, configHome)
 }
 
 // Config will return the correct input path given any input.
@@ -38,11 +43,7 @@ func init() {
 // will be appended.
 func Config(path string) string {
 	if path == "" {
-		if XDGConfigHome == "" {
-			return filepath.Join(Home, File)
-		}
-
-		return filepath.Join(XDGConfigHome, File)
+		return filepath.Join(ConfigHome, File)
 	}
 
 	expandedPath := expandPath(path)
@@ -62,16 +63,17 @@ func Exercises(path string) string {
 	return expandPath(path)
 }
 
-// Recalculate sets exercism paths based on Home.
-func Recalculate() {
-	if Home == "" {
-		home, err := findHome()
-		if err != nil {
-			panic(err)
-		}
+// Recalculate sets exercism paths
+func Recalculate(home, configHome string) {
+	if home != "" {
 		Home = home
 	}
-	XDGConfigHome = os.Getenv("XDG_CONFIG_HOME")
+	if configHome != "" {
+		ConfigHome = configHome
+	}
+	if ConfigHome == "" {
+		ConfigHome = Home
+	}
 }
 
 // IsDir determines whether the given path is a valid directory path.

paths/paths_test.go

@@ -16,7 +16,7 @@ func TestExercises(t *testing.T) {
 	dir, err := os.Getwd()
 	assert.NoError(t, err)
 	Home = "/test/home"
-	Recalculate()
+	Recalculate(Home, "")
 
 	testCases := []struct {
 		givenPath    string
@@ -39,8 +39,7 @@ func TestConfig(t *testing.T) {
 	dir, err := os.Getwd()
 	assert.NoError(t, err)
 
-	Home = dir
-	Recalculate()
+	Recalculate(dir, dir)
 
 	testCases := []struct {
 		desc         string
@@ -76,8 +75,10 @@ func TestConfig(t *testing.T) {
 }
 
 func TestXDGConfig(t *testing.T) {
-	XDGConfigHome = "/home/user/.xdg_config"
-
-	assert.Equal(t, filepath.Join(XDGConfigHome, File), Config(""))
+	dir, err := os.Getwd()
+	assert.NoError(t, err)
+	xdgConfigHome := "/home/user/.xdg_config"
+	Recalculate(dir, xdgConfigHome)
 
+	assert.Equal(t, filepath.Join(xdgConfigHome, File), Config(""))
 }