fix unit tests and address some comments (kubeflow#1892)

sdk/python/kfp/compiler/_container_builder.py

@@ -41,7 +41,7 @@ def __init__(self, gcs_staging=None, gcr_image_tag=None, namespace=None):
       try:
         gcs_bucket = self._get_project_id()
       except:
-        raise ValueError('Please provide the gcr_staging.')
+        raise ValueError('Cannot get the Google Cloud project ID, please specify the gcs_staging argument.')
       self._gcs_staging = 'gs://' + gcs_bucket + '/' + GCS_STAGING_BLOB_DEFAULT_PREFIX
     else:
       from pathlib import PurePath
@@ -160,7 +160,7 @@ def build(self, local_dir, docker_filename, target_image=None, timeout=1000):
       target_image (str): the target image tag to push the final image.
       timeout (int): time out in seconds. Default: 1000
     """
-    target_image = self._gcr_image_tag if target_image is None else target_image
+    target_image = target_image or self._gcr_image_tag
     # Prepare build context
     with tempfile.TemporaryDirectory() as local_build_dir:
       from ._gcs_helper import GCSHelper

sdk/python/tests/compiler/container_builder_test.py

@@ -21,6 +21,7 @@
 from kfp.compiler._component_builder import ContainerBuilder
 
 GCS_BASE = 'gs://kfp-testing/'
+GCR_IMAGE_TAG = 'gcr.io/kfp-testing/image'
 
 @mock.patch('kfp.compiler._gcs_helper.GCSHelper')
 class TestContainerBuild(unittest.TestCase):
@@ -39,7 +40,7 @@ def test_wrap_dir_in_tarball(self, mock_gcshelper):
         f.write('temporary file two content')
 
       # check
-      builder = ContainerBuilder(gcs_staging=GCS_BASE, namespace='')
+      builder = ContainerBuilder(gcs_staging=GCS_BASE, gcr_image_tag=GCR_IMAGE_TAG, namespace='')
       builder._wrap_dir_in_tarball(temp_tarball, test_data_dir)
     self.assertTrue(os.path.exists(temp_tarball))
     with tarfile.open(temp_tarball) as temp_tarball_handle:
@@ -57,7 +58,7 @@ def test_generate_kaniko_yaml(self, mock_gcshelper):
     test_data_dir = os.path.join(os.path.dirname(__file__), 'testdata')
 
     # check
-    builder = ContainerBuilder(gcs_staging=GCS_BASE, namespace='default')
+    builder = ContainerBuilder(gcs_staging=GCS_BASE, gcr_image_tag=GCR_IMAGE_TAG, namespace='default')
     generated_yaml = builder._generate_kaniko_spec(docker_filename='dockerfile',
                                                    context='gs://mlpipeline/kaniko_build.tar.gz', target_image='gcr.io/mlpipeline/kaniko_image:latest')
     with open(os.path.join(test_data_dir, 'kaniko.basic.yaml'), 'r') as f: