def METHOD_NAME(lock):
    # type: (str) -> VCSArtifact
    lock_file = json_codec.load(lock)
    assert 1 == len(lock_file.locked_resolves)
    locked_resolve = lock_file.locked_resolves[0]
    assert 1 == len(locked_resolve.locked_requirements)
    locked_requirement = locked_resolve.locked_requirements[0]
    assert 0 == len(locked_requirement.additional_artifacts)
    assert isinstance(locked_requirement.artifact, VCSArtifact)
    return locked_requirement.artifact