tests/sources: Test that fetch() is not called for cached sources

tests/sources/no-fetch-cached/files/file

+Hello World!

tests/sources/no-fetch-cached/plugins/sources/always_cached.py

+"""
+always_cached
+=============
+
+This is a test source plugin that is always cached.
+Used to test that BuildStream core does not call fetch() for cached sources.
+
+"""
+
+from buildstream import Consistency, Source
+
+
+class AlwaysCachedSource(Source):
+
+    def configure(self, node):
+        pass
+
+    def preflight(self):
+        pass
+
+    def get_unique_key(self):
+        return None
+
+    def get_consistency(self):
+        return Consistency.CACHED
+
+    def load_ref(self, node):
+        pass
+
+    def get_ref(self):
+        return None
+
+    def set_ref(self, ref, node):
+        pass
+
+    def fetch(self):
+        # Source is always cached, so fetch() should never be called
+        assert False
+
+    def stage(self, directory):
+        pass
+
+
+def setup():
+    return AlwaysCachedSource

tests/sources/no-fetch-cached/project.conf

+# Project with local source plugins
+name: no-fetch-cached
+
+plugins:
+- origin: local
+  path: plugins/sources
+  sources:
+    always_cached: 0

tests/sources/no_fetch_cached.py

+import os
+import pytest
+
+from buildstream import _yaml
+
+from tests.testutils import cli, create_repo
+from tests.testutils.site import HAVE_GIT
+
+DATA_DIR = os.path.join(
+    os.path.dirname(os.path.realpath(__file__)),
+    'no-fetch-cached'
+)
+
+
+##################################################################
+#                              Tests                             #
+##################################################################
+# Test that fetch() is not called for cached sources
+@pytest.mark.skipif(HAVE_GIT is False, reason="git is not available")
+@pytest.mark.datafiles(DATA_DIR)
+def test_no_fetch_cached(cli, tmpdir, datafiles):
+    project = os.path.join(datafiles.dirname, datafiles.basename)
+
+    # Create the repo from 'files' subdir
+    repo = create_repo('git', str(tmpdir))
+    ref = repo.create(os.path.join(project, 'files'))
+
+    # Write out test target with a cached and a non-cached source
+    element = {
+        'kind': 'import',
+        'sources': [
+            repo.source_config(ref=ref),
+            {
+                'kind': 'always_cached'
+            }
+        ]
+    }
+    _yaml.dump(element, os.path.join(project, 'target.bst'))
+
+    # Test fetch of target with a cached and a non-cached source
+    result = cli.run(project=project, args=[
+        'source', 'fetch', 'target.bst'
+    ])
+    result.assert_success()