def METHOD_NAME(self, alg: str, tmp_path: Path) -> None:
    """Test add_file."""
    content = "hello world!"
    test_file0 = tmp_path / "test0.txt"
    test_file0.write_text(content)
    test_file1 = tmp_path / "test1.txt"
    test_file1.write_text(content)
    expected = hashlib.new(alg)
    for test_file in [test_file0, test_file1]:
        expected.update((str(test_file) + "\0").encode())
        expected.update((content + "\0").encode())
    result = FileHash(hashlib.new(alg))
    result.add_files([test_file0, test_file1])
    assert result.digest_size == expected.digest_size
    assert result.digest == expected.digest()
    assert result.hexdigest == expected.hexdigest()