<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def is_train_dir(dir_: str) -> bool: """Test if the given dir contains training artifacts."""

    return path.exists(path.join(dir_, CXF_CONFIG_FILE)) and \
           path.exists(path.join(dir_, CXF_TRACE_FILE)) and \
           path.exists(path.join(dir_, CXF_LOG_FILE))