Documentation of examples of running tests

[griff-rees]

Write out an example of running tests locally via pytest and encourage that for future contributors.

[kallewesterling]

To ease our minds a bit, perhaps we could add something about encouragement of implementing pytest in the codebase in a paragraph in the contributor guide, and then link out to some good tutorials or so on best practices around building unit tests with pytest? It seems beyond the scope of the contribution guide for alto2txt to include anything extremely long, but perhaps an example of how we've implemented pytest thus far could be included?

For example, an explanation of this (and how it's using both pytest and icecream?):

def test_output_dir_args(tmp_path):
    # Use the `tmp_path` fixture to ensure that the so-called "non-existant" dirs aren't
    # later inadvertently created within the repo.

    # Test that a non-existant `txt_out_dir` is created, including if it is a very deeply nested dir.
    # output_dir = tmp_path / "non-existant-output-dir"
    output_dirs_list = [
        tmp_path / "non-existant-output-dir",
        tmp_path
        / "a"
        / "b"
        / "c"
        / "d"
        / "very"
        / "deeply"
        / "nested"
        / "nonexistent"
        / "dir",
    ]

    for output_dir in output_dirs_list:
        assert not output_dir.exists()
        sys.argv[1:] = ["demo-files", str(output_dir)]
        extract_publications_text.main()
        assert output_dir.exists()

    # Check that passing a existing file (rather than a dir) is caught
    file_not_dir = tmp_path / "output-file.txt"
    file_not_dir.touch()

    with pytest.raises(AssertionError) as ae:
        sys.argv[1:] = ["demo-files", str(file_not_dir)]
        extract_publications_text.main()

    assert ae.match("output-file.txt")
    assert ae.match("txt_out_dir.+not a directory")