Improve pytest.approx error messages readability #8335
Description
Hey all. I think that as important as getting PASSED on our tests, it is important to get useful messages when the tests FAIL. That being said...
What's the problem this feature will solve?
While comparing numerical data with pytest.approx, I find the messages a bit hard to read when we are comparing big enough numpy arrays. Example:
def test_bla():
import numpy as np
a = np.linspace(0, 100, 20)
b = np.linspace(0, 100, 20)
a[10] += 0.5
assert a == pytest.approx(b)The error message:
> assert a == pytest.approx(b)
E assert array([ 0. , 5.26315789, 10.52631579, 15.78947368,\n 21.05263158, 26.31578947, 31.57894737, 36.84210526,\n 42.10526316, 47.36842105, 53.13157895, 57.89473684,\n 63.15789474, 68.42105263, 73.68421053, 78.94736842,\n 84.21052632, 89.47368421, 94.73684211, 100. ]) == approx([0.0 ± 1.0e-12, 5.2631578947368425 ± 5.3e-06, 10.526315789473685 ± 1.1e-05, 15.789473684210527 ± 1.6e-05, 21.05263157894737 ± 2.1e-05, 26.315789473684212 ± 2.6e-05, 31.578947368421055 ± 3.2e-05, 36.8421052631579 ± 3.7e-05, 42.10526315789474 ± 4.2e-05, 47.36842105263158 ± 4.7e-05, 52.631578947368425 ± 5.3e-05, 57.89473684210527 ± 5.8e-05, 63.15789473684211 ± 6.3e-05, 68.42105263157896 ± 6.8e-05, 73.6842105263158 ± 7.4e-05, 78.94736842105263 ± 7.9e-05, 84.21052631578948 ± 8.4e-05, 89.47368421052633 ± 8.9e-05, 94.73684210526316 ± 9.5e-05, 100.0 ± 1.0e-04])
This is the main example I want to solve, although I've implemented a solution for other cases.
Describe the solution you'd like
Would be nice to have something like this:
> assert a == pytest.approx(b)
E assert comparison failed for 1 values:
E Index | Obtained | Expected
E (10,) | 53.131578947368425 | 52.631578947368425 ± 5.3e-05
Alternative Solutions
I haven't tried any workaround. But I implemented a solution, using pytest_assertrepr_compare. It is in this gist: https://gist.github.com/tarcisiofischer/cab56a5eb65aaa03bdbb4d206f1d49f0
Examples:
> assert [1, 2, 3, 4] == pytest.approx([1, 3, 3, 5])
E assert comparison failed for 2 values:
E Index | Obtained | Expected
E 1 | 2 | 3 ± 3.0e-06
E 3 | 4 | 5 ± 5.0e-06
> assert 1.0 == pytest.approx(2.0)
E assert comparison failed
E Obtained: 1.0
E Expected: 2.0 ± 2.0e-06
> assert {'a': 1, 'b': 3} == pytest.approx({'a': 1.7, 'b': 3})
E assert comparison failed for 1 values:
E Index | Obtained | Expected
E a | 1 | 1.7 ± 1.7e-06
A big one (sorry for the dump)
> assert np.array([
[
[1.1987311, 12412342.3],
[3.214143244, 1423412423415.677]
], [
[1, 2],
[3, 219371297321973]
]
]) == pytest.approx(
np.array([
[
[1.12313, 12412342.3],
[3.214143244, 534523542345.677]
], [
[1, 2],
[3, 7]
]
])
)
E assert comparison failed for 3 values:
E Index | Obtained | Expected
E (0, 0, 0) | 1.1987311 | 1.12313 ± 1.1e-06
E (0, 1, 1) | 1423412423415.677 | 534523542345.677 ± 5.3e+05
E (1, 1, 1) | 219371297321973.0 | 7.0 ± 7.0e-06
Additional context
Just to mention, I didn't find any similar issue, so I'm starting a new one. The following issue has similar title, but it is completely different: #6985
Please, let me know if you guys like my proposal, and feel free to suggest improvements - I'll be happy to hear ideas.
Also, feel free to disagree and close this proposal, so I will just move my code to my project's conftest.py ;)