def METHOD_NAME(
    testdata_dir: pathlib.Path, tmp_trestle_dir: pathlib.Path, monkeypatch: MonkeyPatch
) -> None:
    """Test execution of assemble plan fails."""
    def execute_mock(*args, **kwargs):
        raise err.TrestleError('execution failed')
    test_data_source = testdata_dir / 'split_merge/step4_split_groups_array/catalogs'
    catalogs_dir = pathlib.Path('catalogs/')
    # Copy files from test/data/split_merge/step4
    shutil.rmtree(catalogs_dir)
    shutil.rmtree(pathlib.Path('dist'))
    shutil.copytree(test_data_source, catalogs_dir)
    monkeypatch.setattr(Plan, 'execute', execute_mock)
    with pytest.raises(err.TrestleError):
        AssembleCmd().assemble_model(
            'catalog', argparse.Namespace(trestle_root=tmp_trestle_dir, name='mycatalog', extension='json', verbose=1)
        )