Allow override required parameters

cloud_build/cloud_build.py

@@ -216,6 +216,12 @@ class CB:
             msg = f'Could not read config file `{e.filename}`: {e.strerror}'
             raise Error(msg)
 
+        def lazy_get_raises(key):
+            if key in override:
+                return override[key]
+            else:
+                return cfg[key]
+
         self.mkimage_profiles_git = self.expand_path(
             cfg.get('mkimage_profiles_git', '')
         )
@@ -260,9 +266,9 @@ class CB:
             self.key = '{:X}'.format(self.key)
 
         try:
-            self._remote = self.expand_path(cfg['remote'])
-            self._images = cfg['images']
-            self._branches = cfg['branches']
+            self._remote = self.expand_path(lazy_get_raises('remote'))
+            self._images = lazy_get_raises('images')
+            self._branches = lazy_get_raises('branches')
             for _, branch in self._branches.items():
                 branch['arches'] = {k: {} if v is None else v
                                     for k, v in branch['arches'].items()}

tests/test_errors.py

@@ -60,6 +60,24 @@ class TestErrors(TestCase):
             self.kwargs.update(config=self.config)
             self.assertRaisesRegex(Error, regex, CB, **self.kwargs)
 
+    def test_override_required_parameters_in_config(self):
+        self.config = tempfile.mktemp(prefix='cb_conf')
+        config_override = {
+            'remote': '/var/empty',
+            'images': {},
+            'branches': {},
+        }
+        with open('tests/minimal_config.yaml') as f:
+            cfg = yaml.safe_load(f)
+
+        for parameter in ['remote', 'images', 'branches']:
+            with open(self.config, 'w') as f:
+                yaml.safe_dump(update(cfg, {parameter: None}), f)
+
+            self.kwargs.update(config=self.config)
+            self.kwargs.update(config_override=config_override)
+            CB(**self.kwargs)
+
     def test_run_already_running(self):
         self.kwargs.update(config='tests/minimal_config.yaml')
         cb = CB(**self.kwargs)  # noqa F841