add unit tests for model container

tests/test_abstract_model_container.py

@@ -0,0 +1,39 @@
+from collections.abc import Sequence
+
+from stpipe.container import AbstractModelContainer
+
+
+class BadContainer(Sequence):
+    def __getitem__(self):
+        pass
+
+    def __len__(self):
+        pass
+
+    def save(self, path, save_model_func):
+        pass
+
+    @staticmethod
+    def read_asn(filepath):
+        pass
+
+    def from_asn(self, asn_data, asn_file_path=None):
+        pass
+
+
+class GoodContainer(BadContainer):
+    @property
+    def crds_observatory(self):
+        return ""
+
+
+def test_good_container():
+    assert issubclass(GoodContainer, AbstractModelContainer)
+    gc = GoodContainer()
+    assert isinstance(gc, AbstractModelContainer)
+
+
+def test_bad_container():
+    assert not issubclass(BadContainer, AbstractModelContainer)
+    bc = BadContainer()
+    assert not isinstance(bc, AbstractModelContainer)