test: add unit tests for APIDbtRunner manifest caching

Cover three scenarios:
- manifest is cached after the first successful invocation
- manifest is not cached when invocation fails
- cached manifest is reused on subsequent calls

Author: dtaniwaki

tests/unit/clients/dbt_runner/test_api_dbt_runner.py

@@ -0,0 +1,89 @@
+from contextlib import contextmanager
+from unittest import mock
+
+from dbt.cli.main import dbtRunnerResult
+
+from elementary.clients.dbt.api_dbt_runner import APIDbtRunner
+
+
+def _make_result(success=True, exception=None):
+    return dbtRunnerResult(
+        success=success,
+        result=None,
+        exception=exception,
+    )
+
+
+def _make_runner():
+    runner = APIDbtRunner.__new__(APIDbtRunner)
+    runner._manifest = None
+    runner.project_dir = "/tmp/fake"
+    runner.env_vars = None
+    runner.raise_on_failure = False
+    return runner
+
+
+@contextmanager
+def _noop_context(*args, **kwargs):
+    yield
+
+
+_PATCH_CHDIR = mock.patch("elementary.clients.dbt.api_dbt_runner.with_chdir", _noop_context)
+_PATCH_ENV = mock.patch("elementary.clients.dbt.api_dbt_runner.env_vars_context", _noop_context)
+
+
+@_PATCH_ENV
+@_PATCH_CHDIR
+@mock.patch("elementary.clients.dbt.api_dbt_runner.dbtRunner")
+def test_manifest_cached_after_first_success(mock_dbt_runner_cls):
+    fake_manifest = object()
+    mock_instance = mock.MagicMock()
+    mock_instance.invoke.return_value = _make_result(success=True)
+    mock_instance.manifest = fake_manifest
+    mock_dbt_runner_cls.return_value = mock_instance
+
+    runner = _make_runner()
+    runner._inner_run_command(["run-operation", "foo"], quiet=True, log_output=False, log_format="json")
+
+    assert runner._manifest is fake_manifest
+    mock_dbt_runner_cls.assert_called_once_with(manifest=None, callbacks=mock.ANY)
+
+
+@_PATCH_ENV
+@_PATCH_CHDIR
+@mock.patch("elementary.clients.dbt.api_dbt_runner.dbtRunner")
+def test_manifest_not_cached_on_failure(mock_dbt_runner_cls):
+    mock_instance = mock.MagicMock()
+    mock_instance.invoke.return_value = _make_result(success=False)
+    mock_instance.manifest = object()
+    mock_dbt_runner_cls.return_value = mock_instance
+
+    runner = _make_runner()
+    runner._inner_run_command(["run-operation", "foo"], quiet=True, log_output=False, log_format="json")
+
+    assert runner._manifest is None
+
+
+@_PATCH_ENV
+@_PATCH_CHDIR
+@mock.patch("elementary.clients.dbt.api_dbt_runner.dbtRunner")
+def test_cached_manifest_reused_on_subsequent_calls(mock_dbt_runner_cls):
+    fake_manifest = object()
+    mock_instance = mock.MagicMock()
+    mock_instance.invoke.return_value = _make_result(success=True)
+    mock_instance.manifest = fake_manifest
+    mock_dbt_runner_cls.return_value = mock_instance
+
+    runner = _make_runner()
+
+    runner._inner_run_command(["run-operation", "foo"], quiet=True, log_output=False, log_format="json")
+    assert runner._manifest is fake_manifest
+
+    new_manifest = object()
+    mock_instance.manifest = new_manifest
+    mock_dbt_runner_cls.reset_mock()
+
+    runner._inner_run_command(["run-operation", "bar"], quiet=True, log_output=False, log_format="json")
+
+    mock_dbt_runner_cls.assert_called_once_with(manifest=fake_manifest, callbacks=mock.ANY)
+    assert runner._manifest is fake_manifest