Using with `matplotlib.testing.decorators.image_comparison`

まず src/mplfinance/_styles.py、特に _apply_mpfstyle を読み、matplotlib.testing.setup() および set_font_settings_for_testing() と比較してください。画像比較テストを確認し、各テストでカスタムスタイルを渡すことなく、ローカルの Dev Containers と GitHub Actions の間でレンダリングされるフォントの一貫性を保てるアプローチを判断してください。既存のベースライン比較が両方の環境で成功すれば完了です。

The problem is that the baseline images generated locally (in a Dev Container) don't match the ones on CI (GitHub Actions running the latest Ubuntu LTS) and thus my tests fail. When I compared the images I figured out that different fonts are being used: CI's Ubuntu has more fonts pre-installed than a Dev Container so the text was rendered with Liberation Sans instead of DejaVu Sans.

To quick fix it:

1. Install Liberation fonts locally
   sudo apt install fonts-liberation
2. Drop matplotlib fonts cache (file location and name can be different)
   rm ~/.cache/matplotlib/fontlist-v330.json
3. Re-generate baseline images

Also to find a solution that won't fail when some font is added/removed locally/remotely, I dug deeper and figured out that matpltolib has a solution for this well-known issue: matplotlib.testing.setup() that calls set_font_settings_for_testing() that sets font.family to DejaVu Sans.

But for mplfinance that makes no difference because the font.family gets overridden by _apply_mpfstyle call. For example, the default style sets it to sans-serif (comes from base_mpl_style='seaborn-darkgrid'), and then nobody knows which font maptlotlib is going to use for rendering.

Here I came up with two solutions:

pytest fixture

Pros:

• uses only public API

Cons:

• need to pass to every .plot(...)

@pytest.fixture
def mpf_style():
    return mpf.make_mpf_style(
        base_mpf_style="default", rc={"font.family": "DejaVu Sans"}
    )

@image_comparison(baseline_images=["test.png"])
def test(mpf_style):
  mpf.plot(..., style=mpf_style)

pytest before-all hook that mutates default style

Pros:

• all the existing tests left untouched
• never forget passing style=... in new ones

Cons:

• gets broken on the underlying mplfinance implementation changes

def pytest_configure() -> None:
    mpf._styledata.default.style["rc"].append(("font.family", "DejaVu Sans"))