TST: Add unit test and testfile for enums

unittests/json-schema-models/datamodel_enum_prop.schema.json

+{
+    "title": "Dataset",
+    "description": "Some description",
+    "type": "object",
+    "properties": {
+        "license": {
+            "type": "string",
+            "enum": ["CC-BY", "CC-BY-SA", "CC0", "restricted access"]
+        }
+    },
+    "required": ["license"]
+}

unittests/test_json_schema_model_parser.py

@@ -126,3 +126,25 @@ def test_required_no_list():
             os.path.join(FILEPATH,
                          "datamodel_required_no_list.schema.json"))
     assert "'Dataset' is not of type 'array'" in str(err.value)
+
+
+def test_enum():
+    """Enums are represented in references to records of a specific type."""
+    # @author Florian Spreckelsen
+    # @date 2022-03-16
+
+    model = parse_model_from_json_schema(os.path.join(
+        FILEPATH, "datamodel_enum_prop.schema.json"))
+    licenses = ["CC-BY", "CC-BY-SA", "CC0", "restricted access"]
+    for name in ["Dataset", "license"] + licenses:
+        assert name in model
+
+    assert isinstance(model["Dataset"], db.RecordType)
+    assert model["Dataset"].get_property("license") is not None
+    assert model["Dataset"].get_property("license").datatype == "license"
+    assert isinstance(model["license"], db.RecordType)
+
+    for name in licenses:
+        assert isinstance(model[name], db.Record)
+        assert len(model[name].parents) == 1
+        assert model[name].has_parent(model["license"])