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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _validate(wdl_file):
 """Run validation on the generated WDL output using wdltool. """

    start_dir = os.getcwd()
    os.chdir(os.path.dirname(wdl_file))
    print("Validating", wdl_file)
    subprocess.check_call(["wdltool", "validate", wdl_file])
    os.chdir(start_dir)