Code Coverage and Ternary Operators

Question

Consider we have this function under test located in the module.py:

def f(a, b):
    return (a - b) if a > b else 1 / 0

And, we have the following test case in the test_module.py:

from unittest import TestCase

from module import f


class ModuleTestCase(TestCase):
    def test_a_greater_than_b(self):
        self.assertEqual(f(10, 5), 5)

If we run tests with pytest with the enabled "branch coverage" with the HTML output reporting:

pytest test_module.py --cov=. --cov-branch --cov-report html

The report is going to claim 100% branch coverage with all the "partial" branches covered:

But, we clearly have not covered the else 1 / 0 part at all.

Is there a way to improve reporting to see the non-covered parts of the ternary operators?

Unlike the keyword version the operator version of if / else is not a control structure but a boolean operation. The actual control structure is hidden in the implementation of the operation, out of the sight of coverage. I agreed that it would be a good idea to have that implemented into the coverage package. — Klaus D.
– Klaus D., Commented Dec 24, 2017 at 5:09

blueyed · Accepted Answer · 2020-10-27 17:41:09Z

14

+50

Branch coverage can only measure branching from one line to another, since Python's trace facility currently only supports per-line tracing. Python 3.7 introduces some bytecode-level tracing, but it would require significant work to make use of it.

https://github.com/nedbat/coveragepy/issues/509 is an issue about this.

edited Oct 27, 2020 at 17:41

blueyed

27.9k4 gold badges83 silver badges71 bronze badges

answered Dec 25, 2017 at 23:29

Ned Batchelder

378k77 gold badges583 silver badges675 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Axel Over a year ago

Now that Python 3.7 is in pre-release, shouldn't the referenced issue be reopened (I ask because I see you are the maintainer)? PS. "opened" != "solved right away", but it is surely an important feature, no?

Ned Batchelder Over a year ago

It would be better to discuss the issue on the issue, no?

Collectives™ on Stack Overflow

Code Coverage and Ternary Operators

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related