--- a
+++ b/tests/functional/test_test_connection.py
@@ -0,0 +1,7 @@
+def test_test_connection(mssql_database, call_cli):
+    env = {
+        "BACKEND": "ehrql.backends.tpp.TPPBackend",
+        "DATABASE_URL": mssql_database.host_url(),
+    }
+    captured = call_cli("test-connection", environ=env)
+    assert "SUCCESS" in captured.out