Add constraints test with custom operator

test/test.py

@@ -50,6 +50,9 @@ class TestPipeline(unittest.TestCase):
             verbosity=0,
             **self.default_test_kwargs,
             procs=0,
+            # Test custom operators with constraints:
+            nested_constraints={"square_op": {"square_op": 3}},
+            constraints={"square_op": 10},
         )
         model.fit(self.X, y)
         equations = model.equations