Add explicit model registration parser test

tests/test_model_registration_parser.py

@@ -0,0 +1,28 @@
+import yaml
+
+from nomenclature import parse_model_registration
+
+from conftest import TEST_DATA_DIR
+
+
+def test_parse_model_registration(tmp_path):
+    parse_model_registration(
+        TEST_DATA_DIR / "region_aggregation" / "excel_model_registration.xlsx", tmp_path
+    )
+
+    # Test model mapping
+    with open(tmp_path / "Model 1.1_mapping.yaml", "r") as file:
+        obs_model_mapping = yaml.safe_load(file)
+    with open(
+        TEST_DATA_DIR / "region_aggregation" / "excel_mapping_reference.yaml", "r"
+    ) as file:
+        exp_model_mapping = yaml.safe_load(file)
+    assert obs_model_mapping == exp_model_mapping
+
+    # Test model regions
+    with open(tmp_path / "Model 1.1_regions.yaml", "r") as file:
+        obs_model_regions = yaml.safe_load(file)
+    exp_model_regions = [
+        {"Model 1.1": ["Model 1.1|Region 1", "Region 2", "Model 1.1|Region 3"]}
+    ]
+    assert obs_model_regions == exp_model_regions