morphologyfactory: refactor chunk bdeps exceptions

This creates a small exception hierarchy for failures to validate
stratum morphologies. This is currently a line rather than a tree,
but it will be expanded later in the patch series.

This also adds test coverage for chunk build dependencies being
omitted.

2 files changed, 30 insertions, 6 deletions

diff --git a/morphlib/morphologyfactory.py b/morphlib/morphologyfactory.py
index d0d9ea04..394d186a 100644
--- a/morphlib/morphologyfactory.py
+++ b/morphlib/morphologyfactory.py
@@ -36,6 +36,17 @@ class NotcachedError(MorphologyFactoryError):
                   "remote cache specified" % repo_name)
 
 
+class StratumError(MorphologyFactoryError):
+    pass
+
+
+class NoChunkBuildDependsError(StratumError):
+    def __init__(self, stratum, chunk):
+        StratumError.__init__(
+            self, 'No build dependencies in stratum %s for chunk %s '
+                  '(build-depends is a mandatory field)' % (stratum, chunk))
+
+
 class MorphologyFactory(object):
 
     '''An way of creating morphologies which will provide a default'''
@@ -136,14 +147,10 @@ class MorphologyFactory(object):
     def _check_and_tweak_stratum(self, morphology, reponame, sha1, filename):
         '''Check and tweak a stratum morphology.'''
 
-        for source in morphology['chunks']:  # pragma: no cover
+        for source in morphology['chunks']:
             if source.get('build-depends', None) is None:
                 name = source.get('name', source.get('repo', 'unknown'))
-                raise morphlib.Error('No build dependencies '
-                                     'stratum %s for chunk %s '
-                                     '(build-depends is a mandatory '
-                                     'field)' %
-                                     (filename, name))
+                raise NoChunkBuildDependsError(filename, name)
 
         morphology.builds_artifacts = [morphology['name']]
         morphology.needs_artifact_metadata_cached = True
diff --git a/morphlib/morphologyfactory_tests.py b/morphlib/morphologyfactory_tests.py
index b1a6a621..7a3dc343 100644
--- a/morphlib/morphologyfactory_tests.py
+++ b/morphlib/morphologyfactory_tests.py
@@ -59,6 +59,18 @@ class FakeLocalRepo(object):
                 "name": "stratum",
                 "kind": "stratum"
             }''',
+        'stratum-no-chunk-bdeps.morph': '''{
+                "name": "stratum-no-chunk-bdeps",
+                "kind": "stratum",
+                "chunks": [
+                    {
+                        "name": "chunk",
+                        "repo": "test:repo",
+                        "ref": "sha1",
+                        "build-mode": "bootstrap"
+                    }
+                ]
+            }''',
         'system.morph': '''{
                 "name": "system",
                 "kind": "system",
@@ -261,3 +273,8 @@ class MorphologyFactoryTests(unittest.TestCase):
         self.assertRaises(morphlib.Error, self.mf.get_morphology,
                           'reponame', 'sha1', 'parse-error.morph')
 
+    def test_fails_on_no_chunk_bdeps(self):
+        self.assertRaises(morphlib.morphologyfactory.NoChunkBuildDependsError,
+                          self.mf.get_morphology, 'reponame', 'sha1',
+                          'stratum-no-chunk-bdeps.morph')
+