Refactor test to use mock

repo2docker/app.py

@@ -744,8 +744,6 @@ class Repo2Docker(Application):
                 else:
                     picked_buildpack = self.default_buildpack()
 
-                self._picked_buildpack = picked_buildpack
-
                 picked_buildpack.appendix = self.appendix
                 picked_buildpack.labels['repo2docker.version'] = self.version
                 picked_buildpack.labels['repo2docker.repo'] = self.repo

tests/test_labels.py

@@ -2,6 +2,7 @@
 Test if labels are supplied correctly to the container
 """
 import time
+from unittest.mock import Mock
 from repo2docker.app import Repo2Docker
 from repo2docker.buildpacks import BuildPack
 from repo2docker import __version__
@@ -19,21 +20,26 @@ def test_buildpack_labels_rendered():
 
 @pytest.mark.parametrize('ref', ['some-branch', None])
 def test_labels(ref, tmpdir):
-    app = Repo2Docker()
     repo = str(tmpdir)
     if ref is not None:
         argv = ['--ref', ref, repo]
     else:
         argv = [repo]
+
+    app = Repo2Docker()
+    # Add mock BuildPack to app
+    mock_buildpack = Mock()
+    mock_buildpack.return_value.labels = {}
+    app.buildpacks = [mock_buildpack]
+
     app.initialize(argv)
     app.build = False
     app.run = False
     app.start()
-    labels = app._picked_buildpack.labels
     expected_labels = {
         'repo2docker.ref': ref,
         'repo2docker.repo': repo,
         'repo2docker.version': __version__,
     }
 
-    assert labels == expected_labels
+    assert mock_buildpack().labels == expected_labels