Use try and except to catch metabolites that are missing

src/memote/suite/tests/test_consistency.py

@@ -154,12 +154,16 @@ def test_detect_energy_generating_cycles(model, met):
 
     """
     ann = test_detect_energy_generating_cycles.annotation
+    # Test if the metabolite is present in the model.
     main_comp = helpers.find_compartment_id_in_model(model, "c")
-    if helpers.find_met_in_model(model, met, main_comp)[0] is None:
+    try:
+        helpers.find_met_in_model(model, met, main_comp)[0]
+    except:
         pytest.skip(
             "This test has been skipped since metabolite {} could "
             "not be found in the model.".format(met)
         )
+    # If the metabolite is present, carry out the test.
     ann["data"][met] = consistency.detect_energy_generating_cycles(model, met)
     # Report the number of cycles scaled by the number of reactions.
     ann["metric"][met] = len(ann["data"][met]) / len(model.reactions)