Surface the error to the user when a module dependency can't be found

module_build_service/resolver/DBResolver.py

@@ -48,7 +48,7 @@ class DBResolver(GenericResolver):
         :param context: a string of the module's context. When None, all contexts will
             be returned.
         :kwarg strict: Normally this function returns [] if no module can be
-            found.  If strict=True, then a ValueError is raised.
+            found.  If strict=True, then a UnprocessableEntity is raised.
         :return: List of Modulemd metadata instances matching the query
         """
         with models.make_session(self.config) as session:
@@ -63,8 +63,8 @@ class DBResolver(GenericResolver):
                     "This combination of name/stream/version/context is not implemented")
 
             if not builds and strict:
-                raise ValueError("Cannot find any module build for %s:%s "
-                                 "in MBS database" % (name, stream))
+                raise UnprocessableEntity(
+                    "Cannot find any module builds for %s:%s" % (name, stream))
             return [build.mmd() for build in builds]
 
     def get_module_tag(self, name, stream, version, context, strict=False):

tests/staged_data/testmodule-no-deps.yaml

@@ -0,0 +1,17 @@
+document: modulemd
+version: 1
+data:
+    summary: A test module in all its beautiful beauty
+    description: >-
+        This module demonstrates how to write simple modulemd files And
+        can be used for testing the build and release pipeline.
+    license:
+        module: [ MIT ]
+    dependencies:
+        buildrequires:
+            chineese_food: good
+        requires:
+            noodles: lomein
+    references:
+        community: https://docs.pagure.org/modularity/
+        documentation: https://fedoraproject.org/wiki/Fedora_Packaging_Guidelines_for_Modules

tests/test_views/test_views.py

@@ -592,6 +592,25 @@ class TestViews:
         }
         assert data == expected_error
 
+    @patch('module_build_service.auth.get_user', return_value=user)
+    @patch('module_build_service.scm.SCM')
+    def test_submit_build_dep_not_present(self, mocked_scm, mocked_get_user):
+        FakeSCM(mocked_scm, 'testmodule', 'testmodule-no-deps.yaml',
+                '620ec77321b2ea7b0d67d82992dda3e1d67055b4')
+
+        rv = self.client.post('/module-build-service/1/module-builds/', data=json.dumps(
+            {'branch': 'master',
+             'scmurl': ('git://pkgs.stg.fedoraproject.org/modules/testmodule.git?'
+                        '#68931c90de214d9d13feefbd35246a81b6cb8d49')}))
+        data = json.loads(rv.data)
+        assert rv.status_code == 422
+        expected_error = {
+            'error': 'Unprocessable Entity',
+            'message': 'Cannot find any module builds for chineese_food:good',
+            'status': 422
+        }
+        assert data == expected_error
+
     @patch('module_build_service.auth.get_user', return_value=user)
     @patch('module_build_service.scm.SCM')
     def test_submit_build_rebuild_strategy_override_not_allowed(self, mocked_scm, mocked_get_user):