Added StepAction test to highlight issue with apply and _apply

Signed-off-by: Anthony Charlton <anthony.charlton@zepben.com>

Author: charlta

test/services/network/tracing/traversal/test_step_action.py

@@ -0,0 +1,50 @@
+#  Copyright 2025 Zeppelin Bend Pty Ltd
+#  This Source Code Form is subject to the terms of the Mozilla Public
+#  License, v. 2.0. If a copy of the MPL was not distributed with this
+#  file, You can obtain one at https://mozilla.org/MPL/2.0/.
+from _pytest.python_api import raises
+
+from zepben.evolve import StepAction, StepContext
+from zepben.evolve.services.network.tracing.traversal.step_action import T
+
+
+class TestStepAction:
+
+    def test_can_apply_lambda(self):
+        """Make sure we can use a lambda as the StepAction"""
+        captured = []
+        step_action = StepAction(lambda it, ctx: captured.append((it, ctx)))
+
+        expected_item = 1
+        expected_ctx = StepContext(is_start_item=True, is_branch_start_item=False)
+
+        step_action.apply(expected_item, expected_ctx)
+
+        assert captured == [(expected_item, expected_ctx)]
+
+    def test_cant_override_apply(self):
+        """This is testing that if you ignore the @final on apply, you will get an exception."""
+        with raises(Exception, match="method 'apply' should not be directly overridden, override '_apply' instead."):
+            class MyStepAction(StepAction):
+
+                # noinspection PyFinal
+                def apply(self, item: T, context: StepContext):
+                    pass
+
+    def test_can_apply_descendant(self):
+        """Simulate someone doing what the exception told you to do"""
+        captured = []
+
+        class MyStepAction(StepAction):
+
+            def _apply(self, item: T, context: StepContext):
+                captured.append((item, context))
+
+        step_action = MyStepAction()
+
+        expected_item = 1
+        expected_ctx = StepContext(is_start_item=True, is_branch_start_item=False)
+
+        step_action.apply(expected_item, expected_ctx)
+
+        assert captured == [(expected_item, expected_ctx)]