Refactor and add unit test

Author: jonathanedey

firebase_admin/__init__.py

@@ -210,11 +210,12 @@ def __init__(self, name, credential, options):
         self._name = name
 
         if isinstance(credential, GoogleAuthCredentials):
-            credential = credentials._ExternalCredentials(credential)
-        if not isinstance(credential, credentials.Base):
+            self._credential = credentials._ExternalCredentials(credential) # pylint: disable=protected-access
+        elif isinstance(credential, credentials.Base):
+            self._credential = credential
+        else:
             raise ValueError('Illegal Firebase credential provided. App must be initialized '
                              'with a valid credential instance.')
-        self._credential = credential
         self._options = _AppOptions(options)
         self._lock = threading.RLock()
         self._services = {}

tests/test_app.py

@@ -246,6 +246,16 @@ def test_non_default_app_init(self, app_credential):
         with pytest.raises(ValueError):
             firebase_admin.initialize_app(app_credential, name='myApp')
 
+    def test_app_init_with_google_auth_cred(self):
+        cred = testutils.MockGoogleCredential()
+        assert isinstance(cred, credentials.GoogleAuthCredentials)
+        app = firebase_admin.initialize_app(cred)
+        assert cred is app.credential.get_credential()
+        assert isinstance(app.credential, credentials.Base)
+        assert isinstance(app.credential, credentials._ExternalCredentials)
+        with pytest.raises(ValueError):
+            firebase_admin.initialize_app(app_credential)
+
     @pytest.mark.parametrize('cred', invalid_credentials)
     def test_app_init_with_invalid_credential(self, cred):
         with pytest.raises(ValueError):