Naming: From Liability to Asset

There are only two hard things in Computer Science: cache invalidation and naming things.

-- Phil Karlton (via Martin Fowler)

In the last section, using trickles(no_override=True) allowed us to restrict the test case we've been working on to testing one function at a time. This can help keep tests organized and focused, as all the tests that have to do with some function are all bundled together, and different functions can get their own files.

But there's a major drawback here: naming. Right now it's fine. is_bread() is tested in test_is_bread.py. But what if we brilliantly renamed the function to affirm_breadness? Discoverability would wither and life would grow confusing.

pytest_embrace has another feature, similar to trickles(), that helps use filenames as data: derive_from_filename(). It is another wrapper around dataclasses.field. By default, it extracts the substring in the filename that follows the word test_.

That means for test_is_bread.py, we could extract is_bread, which is a good start, but we need a specific function, not a string.

Luckily, derive_from_filename takes a parse argument that lets us take that substring and do anything we want with it, ultimately returning any value.

In our case, it can be used to find the right crud function based on the name of the test file.

test_is_bread.py

import crud  # the namespace we test against


@dataclass
class CrudTestCase:
    args: tuple[Any, ...]
    assert_return: Any
    should: str  # assertion message
    seed_data: list[tuple[Any, ...]] = trickles()

    # tada!
    crud_func: Callable[..., Any] = derive_from_filename(
        parse=lambda x: getattr(crud, x)
    )

    def __str__(self) -> str:
        return f"{self.crud_func.__name__}{self.args} -> {self.assert_return}"

And we can remove the crud_func declaration from the test file.

test_is_bread.py

from conftest import CrudTestCase

seed_data = [
    ("mirth", False, "feeling", "prefontal cortex", 5),
    ("fear", False, "feeling", "prefontal cortex", 0),
    ("croissant", True, "food", "france", 4),
]

table = [
    CrudTestCase(
        args=("mirth",),
        assert_return=False,
        should="Mirth is a feeling, not bread.",
    ),
    CrudTestCase(
        args=("croissant",),
        assert_return=True,
        should="A croissant is tasty bread.",
    ),
]


def test(crud_case):
    ...

Now, even the name of the file will change over time with the system it's testing. And––even better––the naming convention of these test modules is saved from fickle human arbitrariness. 💪🏽