def METHOD_NAME(file, multiline_file):
    # Should create a backup file. This is basically the default
    bak_file = "{}.bak".format(multiline_file)
    file.replace(str(multiline_file), "Etiam", "Salticus")
    assert "Salticus" in multiline_file.read_text()
    assert os.path.exists(bak_file)