Description
Suggestion
Pytest currently doesn't show tolerance when asserting approximate equality on complex numbers. This can make it a little hard to understand just how approx compares complex numbers.
for example, on pytest 5.2.2
> assert 3.0002 + 4.0003 * 1j == approx(3 + 4j)
E assert (3.0002+4.0003j) == (3+4j)
E -(3.0002+4.0003j)
E +(3+4j)
When pytest does comparisons involving complex numbers, it computes the complex different between the two numbers and then asserts that the absolute value of the difference falls below the tolerance (which, for relative tolerance is calculated as a fraction of the absolute value of the value passed to approx).
This means that if you draw a circle around the target point in the complex plane, with a radius equal to the tolerance, the compared value should fall within that circle
given this, I propose adding a tolerance indicator to complex numbers using a polar notation:
> assert 3.0002 + 4.0003 * 1j == approx(3 + 4j)
E assert (3.0002+4.0003j) == (3+4j) ± 5e-06 ∠ ±180°
E -(3.0002+4.0003j)
E +(3+4j) ± 5e-06 ∠ ±180°
in this notation, 5e-06 is the calculated relative tolerance, derived as abs(3+4j) * 1e-06. the ∠ ±180° component is fixed to indicate that the delta between actual and expected is a complex value as well, and that it can have any angle as long as the magnitude is within the tolerance.
Version
* pytest 5.2.2
* python 3.7.3
* ubuntu 19.04