chore: add tests for getCredentialPath (#247)

Adds basic regression tests for the getCredentialPath helper in
credentials.go.

Author: amoeba

auth/credentials_test.go

@@ -20,6 +20,7 @@ import (
 	"net/url"
 	"os"
 	"path/filepath"
+	"runtime"
 	"sync"
 	"testing"
 
@@ -554,3 +555,56 @@ func TestUpdateCreds(t *testing.T) {
 		assert.Equal(t, "test-key", creds[0].ApiKey)
 	})
 }
+
+func TestGetCredentialPath(t *testing.T) {
+	t.Run("honors XDG_DATA_HOME when set to an absolute path", func(t *testing.T) {
+		tmpDir := t.TempDir()
+		t.Setenv("XDG_DATA_HOME", tmpDir)
+
+		path, err := getCredentialPath()
+		require.NoError(t, err)
+		expected := filepath.Join(tmpDir, "dbc", "credentials", "credentials.toml")
+		assert.Equal(t, expected, path)
+	})
+
+	t.Run("errors if XDG_DATA_HOME is set to a relative path", func(t *testing.T) {
+		t.Setenv("XDG_DATA_HOME", "any/relative/path")
+
+		_, err := getCredentialPath()
+		assert.Error(t, err)
+		assert.Contains(t, err.Error(), "path in $XDG_DATA_HOME is relative")
+	})
+
+	t.Run("default behavior for each platform", func(t *testing.T) {
+		switch runtime.GOOS {
+		case "windows":
+			appData := os.Getenv("LocalAppData")
+			if appData == "" {
+				t.Errorf("failed to get LocalAppData")
+			}
+			path, err := getCredentialPath()
+			require.NoError(t, err)
+			assert.Equal(t, filepath.Join(appData, "dbc", "credentials", "credentials.toml"), path)
+
+		case "darwin":
+			userHome, err := os.UserHomeDir()
+			if err != nil {
+				t.Errorf("failed to get user home directory")
+			}
+
+			path, err := getCredentialPath()
+			require.NoError(t, err)
+			assert.Equal(t, filepath.Join(userHome, "Library", "dbc", "credentials", "credentials.toml"), path)
+
+		default:
+			userHome, err := os.UserHomeDir()
+			if err != nil {
+				t.Errorf("failed to get user home directory")
+			}
+
+			path, err := getCredentialPath()
+			require.NoError(t, err)
+			assert.Equal(t, filepath.Join(userHome, ".local", "share", "dbc", "credentials", "credentials.toml"), path)
+		}
+	})
+}