Return empty colors for .cxg v0.0 files (#1441)

* Return empty colors for .cxg v0.0 files

Fixes https://github.com/chanzuckerberg/cellxgene/issues/1440

The CxgAdaptor.get_colors method currently assumes that the .cxg file has
cxg_group_metadata. As a result, the /api/v0.2/colors endpoint always fails for
.cxg v0.0 files.

* Add test fixture

server/data_cxg/cxg_adaptor.py

@@ -195,6 +195,8 @@ class CxgAdaptor(DataAdaptor):
         return diffexp_cxg.diffexp_ttest(self, maskA, maskB, top_n, lfc_cutoff)
 
     def get_colors(self):
+        if self.cxg_version == "0.0":
+            return dict()
         meta = self.open_array("cxg_group_metadata").meta
         return json.loads(meta["cxg_category_colors"]) if "cxg_category_colors" in meta else dict()
 

server/test/test_cxg_adaptor.py

@@ -7,10 +7,14 @@ from server.test.test_datasets.fixtures import pbmc3k_colors
 
 
 class TestCxgAdaptor(unittest.TestCase):
-    def setUp(self):
-        data_locator = f"{PROJECT_ROOT}/server/test/test_datasets/pbmc3k.cxg"
-        config = app_config(data_locator)
-        self.data = CxgAdaptor(DataLocator(data_locator), config)
 
     def test_get_colors(self):
-        self.assertEqual(self.data.get_colors(), pbmc3k_colors)
+        data = self.get_data("pbmc3k.cxg")
+        self.assertDictEqual(data.get_colors(), pbmc3k_colors)
+        data = self.get_data("pbmc3k_v0.cxg")
+        self.assertDictEqual(data.get_colors(), dict())
+
+    def get_data(self, fixture):
+        data_locator = f"{PROJECT_ROOT}/server/test/test_datasets/{fixture}"
+        config = app_config(data_locator)
+        return CxgAdaptor(DataLocator(data_locator), config)