Python CLI program unit testing

Question

I am working on a python Command-Line-Interface program, and I find it boring when doing testings, for example, here is the help information of the program:

Answer 1

I think it's perfectly fine to test functionally on a whole-program level. It's still possible to test one aspect/option per test. This way you can be sure that the program really works as a whole. Writing unit-tests usually means that you get to execute your tests quicker and that failures are usually easier to interpret/understand. But unit-tests are typically more tied to the program structure, requiring more refactoring effort when you internally change things.

Anyway, using py.test, here is a little example for testing a latin1 to utf8 conversion for pyconv::

# content of test_pyconv.py

import pytest

# we reuse a bit of pytest's own testing machinery, this should eventually come
# from a separatedly installable pytest-cli plugin. 
pytest_plugins = ["pytester"]

@pytest.fixture
def run(testdir):
    def do_run(*args):
        args = ["pyconv"] + list(args)
        return testdir._run(*args)
    return do_run

def test_pyconv_latin1_to_utf8(tmpdir, run):
    input = tmpdir.join("example.txt")
    content = unicode("\xc3\xa4\xc3\xb6", "latin1")
    with input.open("wb") as f:
        f.write(content.encode("latin1"))
    output = tmpdir.join("example.txt.utf8")
    result = run("-flatin1", "-tutf8", input, "-o", output)
    assert result.ret == 0
    with output.open("rb") as f:
        newcontent = f.read()
    assert content.encode("utf8") == newcontent

After installing pytest ("pip install pytest") you can run it like this::

$ py.test test_pyconv.py
=========================== test session starts ============================
platform linux2 -- Python 2.7.3 -- pytest-2.4.5dev1
collected 1 items

test_pyconv.py .

========================= 1 passed in 0.40 seconds =========================

The example reuses some internal machinery of pytest's own testing by leveraging pytest's fixture mechanism, see http://pytest.org/latest/fixture.html. If you forget about the details for a moment, you can just work from the fact that "run" and "tmpdir" are provided for helping you to prepare and run tests. If you want to play, you can try to insert a failing assert-statement or simply "assert 0" and then look at the traceback or issue "py.test --pdb" to enter a python prompt.

Answer 2

The short answer is yes, you can use unit tests, and should. If your code is well structured, it should be quite easy to test each component separately, and if you need to to can always mock sys.argv to simulate running it with different arguments.

Answer 3

pytest-console-scripts is a Pytest plugin for testing python scripts installed via console_scripts entry point of setup.py.