feat(test): add tests for the current behaviour

tests/google_big_query/test_google_big_query.py

@@ -852,3 +852,21 @@ def test_optional_fields_validator_for_google_creds_or_jwt():
     }
     # no error raised
     _ = GoogleBigQueryConnector(name='something', jwt_credentials=valid_credentials)
+
+
+def test_get_project_id(
+    connector: GoogleBigQueryConnector, _fixture_credentials: GoogleCredentials
+) -> None:
+    # test get project id with jwt credentials
+    connector.jwt_credentials = JWTCredentials(jwt_token='token', project_id='123')
+    assert connector._get_project_id() == '123'
+
+    # test get project id with credentials
+    connector.jwt_credentials = None
+    connector.credentials = _fixture_credentials
+    connector.credentials.project_id = '456'
+    assert connector._get_project_id() == '456'
+
+    # On ProjectId missing...
+    with pytest.raises(GoogleClientCreationError):
+        connector._get_project_id()