Remove need for date and artifical strain key in metadata

Author: jeromekelleher

sc2ts/dataset.py

@@ -184,11 +184,12 @@ def get_metadata(self, j):
                 d[key] = bool(d[key])
             else:
                 d[key] = str(d[key])
-        if self.date_field is None:
-            raise ValueError("No date field set, cannot get metadata items")
-        # For compatibility in the short term:
-        d["date"] = self.sample_date[j]
-        d["strain"] = self.sample_id[j]
+        if self.date_field is not None:
+            # For compatibility in the short term:
+            d["date"] = self.sample_date[j]
+            # NOTE 'strain' will be removed
+            # https://github.com/tskit-dev/sc2ts/issues/574
+            d["strain"] = self.sample_id[j]
         return d
 
     def __getitem__(self, key):

tests/test_dataset.py

@@ -469,9 +469,8 @@ def test_known(self, fx_dataset):
 
     def test_known_no_date_field(self, fx_dataset):
         ds = sc2ts.Dataset(fx_dataset.path)
-
-        with pytest.raises(ValueError, match="No date field set"):
-            ds.metadata["SRR11772659"]
+        d = ds.metadata["SRR11772659"]
+        assert "strain" not in d
 
     @pytest.mark.parametrize(
         ["chunk_size", "cache_size"],