diff --git a/tests/test_TPI.py b/tests/test_TPI.py
index 972e33f19..d37db5217 100644
--- a/tests/test_TPI.py
+++ b/tests/test_TPI.py
@@ -629,6 +629,7 @@ def test_run_TPI(baseline, param_updates, filename, tmpdir, dask_client):
         (True, {}, filename1),
         (False, param_updates4, filename4),
         (True, param_updates8, filename8),
+        (True, param_updates9, filename9),
     ]
     id_list = [
         "Baseline, balanced budget",
@@ -638,6 +639,7 @@ def test_run_TPI(baseline, param_updates, filename, tmpdir, dask_client):
         "Baseline",
         "Reform, baseline spending",
         "Baseline, Kg>0",
+        "mono tax functions",
     ]