test: add basic AccountRunner test

This test validates that a Command's lifecycle methods are invoked by
the runner: pre_hook_with_context, execute, collect_results, and
post_hook. It also validates that the older pre_hook is still called if
the newer pre_hook_with_context does not exist.

Author: pkazmier

tests/unit/test_runner.py

@@ -0,0 +1,52 @@
+#
+# Copyright 2025 FMR LLC <opensource@fidelity.com>
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+# pylint: disable=redefined-outer-name,missing-docstring
+
+import pytest
+from awsrun.runner import AccountRunner, Command
+from awsrun.session import SessionProvider
+
+
+@pytest.fixture
+def runner(mocker):
+    session_provider = mocker.MagicMock(spec=SessionProvider)
+    return AccountRunner(session_provider)
+
+
+def test_lifecycle_methods(mocker, runner):
+    command = mocker.MagicMock(spec=Command)
+    runner.run(command, ["a", "b"])
+    command.pre_hook_with_context.assert_called()
+    assert command.execute.call_count == 2
+    command.collect_results.assert_called()
+    command.post_hook.assert_called()
+
+
+def test_lifecycle_methods_with_no_accts_to_process(mocker, runner):
+    command = mocker.MagicMock(spec=Command)
+    runner.run(command, [])
+    command.pre_hook_with_context.assert_called()
+    command.execute.assert_not_called()
+    command.collect_results.assert_not_called()
+    command.post_hook.assert_called()
+
+
+def test_pre_hook_with_context(mocker, runner):
+    command = Command()
+    command.pre_hook_with_context = mocker.MagicMock()
+    runner.run(command, [], context="Hello")
+    command.pre_hook_with_context.assert_called_with("Hello")
+
+
+# If no pre_hook_with_context is explicitly defined in a Command, then the
+# default implementation should invoke the older pre_hook method for
+# backwards compatibility.
+def test_backwards_compat_lifecycle_pre_hook(mocker, runner):
+    command = Command()
+    command.pre_hook = mocker.MagicMock()
+    runner.run(command, [])
+    command.pre_hook.assert_called()