added a test for invariant filename

jwst/stpipe/tests/test_utilities.py

@@ -5,6 +5,10 @@
 from jwst.stpipe.utilities import all_steps, NOT_SET
 import jwst.pipeline
 import jwst.step
+import pytest
+from stdatamodels.jwst import datamodels
+from jwst.stpipe.utilities import invariant_filename
+
 from jwst import datamodels as dm
 
 
@@ -54,3 +58,32 @@ def test_record_query_step_status():
     # test query not set
     model3 = dm.MultiSpecModel()
     assert query_step_status(model3, 'test_step') == NOT_SET
+
+# make up a datamodel for testing filename
+@pytest.fixture(scope='function')
+def miri_ifushort():
+    """ Generate input model IFU image """
+
+
+    mirifushort_short = {
+        'detector': 'MIRIFUSHORT',
+        'channel': '12',
+        'band': 'SHORT',
+        'name': 'MIRI'
+
+    }
+    input_model = datamodels.IFUImageModel()
+    input_model.meta.exposure.type = 'MIR_MRS'
+    input_model.meta.instrument._instance.update(mirifushort_short)
+    input_model.meta.filename = 'test1.fits'
+    return input_model
+
+
+def change_name_func(model):
+    model.meta.filename = "changed"
+    return model
+
+def test_invariant_filename(miri_ifushort):
+    invariant_save_func = invariant_filename(change_name_func)
+    output_model = invariant_save_func(miri_ifushort)
+    assert output_model.meta.filename == "test1.fits"