Things I Learned: Using pytest to check stdout from python methods

 So, adding automated remote station location updates to the code that tracks the Reverse Beacon Network spots of the KD0FNR Rockmite has become a bit of an oddysey, but here's more cool stuff:

The output python script new_key_cat.py is supposed to present only lines of output (to stdout) that do not contain keys that already exist in rm_rnb_history_pres.csv. Tests are being built for the script using pytest. pytest mutes stdin because the tests are intended to be automated rather than interactive. This makes sense to me, so I'm changing the method in the script that handles input to look for a file name argument, and if it doesn't have one to use stdin.

The second issue though was how to write an automated test case that looks at stdout. It turns out pytest has that covered. It's all written up at

https://docs.pytest.org/en/7.1.x/how-to/capture-stdout-stderr.html

And here's the pertinent code example from that page:

def test_myoutput(capsys):  # or use "capfd" for fd-level
    print("hello")
    sys.stderr.write("world\n")
    captured = capsys.readouterr()
    assert captured.out == "hello\n"
    assert captured.err == "world\n"
    print("next")
    captured = capsys.readouterr()
    assert captured.out == "next\n"

The test case for new_key_cat specified above will send in a file with two keys that already exist in rm_rnb_history_pres.csv. The test case will check to make sure they are not output by doing the following

def test_new_key_cat_2(capsys):  # or use "capfd" for fd-level
    new_key_cat("testfile_with_existing_keys")
    captured = capsys.readouterr()
    assert not captured.out.find("existing_key_1")

So, if an existing key does turn up in the output, the test case will fail. A more exhaustive test would be to look for all the existing keys as in:

def test_new_key_cat_2(capsys):  # or use "capfd" for fd-level
    new_key_cat("testfile_with_existing_keys")
    captured = capsys.readouterr()
    for entry in make_key_list("rm_rnb_history_pres.csv"):
        assert not captured.out.find(entry)

The documentation for capsys offers far more detail:

https://docs.pytest.org/en/7.1.x/reference/reference.html?highlight=capsys#std-fixture-capsys

I'm kinda falling in love with pytest.

References:

Reverset Beacon Network

githbub repository for the KD0FNR Rockmite Reverse Beacon Network spot tracker