Dedupe spectral plotting tests.

[anntzer]

There was a lot of repeated code in the tests... this shortens
test_axes.py by ~10%(!)

PR Summary

PR Checklist

• Has Pytest style unit tests
• Code is Flake 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way

[efiring]

This is a very welcome clarification and reduction in lines. I noted one point of style (indentation) I would like to see changed, but I won't insist on it.

[efiring]

Style nit-pick, here and below: I think this pattern of out-denting is counterproductive and impairs readability. I hope it doesn't take hold as typical practice.

[anntzer]

I personally dislike out-denting when the delimiter ends up being the sole character(s) on its own line, which is sadly the style used by the sadly (yes, twice) popular black formatter -- it would give you

@image_comparison(
    [
        "specgram_freqs.png",
        "specgram_freqs_linear.png",
        "specgram_noise.png",
        "specgram_noise_linear.png",
    ],
    remove_text=True,
    tol=0.07,
    style="default",
)
def test_specgram():
    """Test axes.specgram in default (psd) mode."""

(yuck! completely ignoring semantics that are not being captured by syntax). I would certainly object to this.

But I do think the style in this PR is a bit more regular than e.g. (A)

@image_comparison(
    ["specgram_freqs.png", "specgram_freqs_linear.png",
     "specgram_noise.png", "specgram_noise_linear.png"],
    remove_text=True, tol=0.07, style="default")
def test_specgram():
    """Test axes.specgram in default (psd) mode."""

(now you do need to edit more things when adding new items to the list -- though the argument is not very strong)
or (B)

@image_comparison(["specgram_freqs.png", "specgram_freqs_linear.png",
                   "specgram_noise.png", "specgram_noise_linear.png"],
                  remove_text=True, tol=0.07, style="default")
def test_specgram():
    """Test axes.specgram in default (psd) mode."""

(losing ~10 characters worth of width on the left of the screen is just silly)

I don't mind changing everything to (A) if we can agree on that, though.

[efiring]

There are many alternative patterns that would, in my view, fit comfortably with Python's basic principle of indentation. If (A) works for you, it is OK for me.

[anntzer]

done