signals_allclose doesn't plot allclose_tolerances

[hunse]

Describe the bug

allclose_tolerances allow backends to override default allclose tolerances for specific tests. These can work with signals_allclose by making it use the allclose fixture rather than np.allclose, but it still uses its default tolerances for plotting. This means that in the plots, the error can look like it's outside tolerances, while the test passes because the error is within the overridden tolerances.

Expected behavior

The allclose fixture supports different tolerances each time it's called, by passing a list to allclose_tolerances. Supporting this seems difficult. More straightforward would be to use _get_allclose_overrides (from pytest-allclose) in signals_allclose, and just use the first (or last?) tolerance if applicable. (I think all our tests that use signals_allclose just have one allclose comparison.)

[tbekolay]

I wonder if we should move the stuff in signals_allclose into the pytest-allclose repo? I.e. give an easy way to generate those plots by passing plot=True or something like that to allclose. If we're going to touch that code anyway, that is.

[hunse]

I like that idea. It definitely seems like a more sensible place for that code to live.