Using with `matplotlib.testing.decorators.image_comparison`

Bắt đầu bằng cách đọc src/mplfinance/_styles.py, đặc biệt là _apply_mpfstyle, và so sánh nó với matplotlib.testing.setup() và set_font_settings_for_testing(). Xem xét các bài kiểm thử so sánh hình ảnh và xác định cách tiếp cận nào giữ cho các font được kết xuất nhất quán giữa các Dev Containers cục bộ và GitHub Actions mà không yêu cầu mỗi bài kiểm thử phải truyền một style tùy chỉnh; được xem là hoàn tất khi các phép so sánh baseline hiện có đều vượt qua trong cả hai môi trường.

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"))