How to unit test this lambda code?

Question

Say, I have something like the following Python code:

try:
    from fabulous.color import fg256
    format_info = lambda x: fg256(63, unicode(x, 'utf-8')).as_utf8
except ImportError:
    format_info = lambda x: '\033[1;30m' + x + '\033[0m'

How can I unit test this?

Is it worth testing?

There is a need to mock the import statement so that both branches are excised. This is fairly trivial -- for example, mock fg256 to have a side effect of raise ImportError .

Matching that the returned string has the right control characters is fine but feels brittle.

Answer 1

What exactly is it that you want to test? You seem to have two unrelated cases here;

• importing fails
• lambda returns correct info

It's not really your responsibility to check that not using your code fails; but if you want to test this nevertheless (perhaps because this is code somebody has posted on a popular forum) I would separate it into two distinct tests.

We don't know what your lambda is supposed to return, but by the looks of it, it should return a string similar to what you assign in the except branch?