1 files changed, 101 insertions, 0 deletions
diff --git a/tests/contrast/test_contrasts.py b/tests/contrast/test_contrasts.py
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+++ b/tests/contrast/test_contrasts.py
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+"""
+    Contrast Tests
+    ~~~~~~~~~~
+
+    Pygments styles should be accessible to people with suboptimal vision.
+    This test ensures that the minimum contrast of styles does not degrade,
+    and that every rule of a new style fulfills the WCAG AA standard.[1]
+
+    [1]: https://www.w3.org/WAI/WCAG21/Understanding/contrast-minimum.html
+"""
+
+import json
+import os
+import sys
+
+import pygments.styles
+import pygments.token
+import wcag_contrast_ratio
+
+JSON_FILENAME = os.path.join(os.path.dirname(__file__), "min_contrasts.json")
+WCAG_AA_CONTRAST = 4.5
+
+
+def hex2rgb(hexstr):
+    hexstr = hexstr.lstrip("#")
+    r = int(hexstr[:2], 16) / 255
+    g = int(hexstr[2:4], 16) / 255
+    b = int(hexstr[4:], 16) / 255
+    return (r, g, b)
+
+
+def get_style_contrasts(style_cls):
+    return [
+        (
+            round(
+                wcag_contrast_ratio.rgb(
+                    hex2rgb(style["bgcolor"] or style_cls.background_color),
+                    hex2rgb(style["color"] or "#000000")
+                    # we default to black because browsers also do
+                ),
+                1,
+            ),
+            ttype,
+        )
+        for ttype, style in style_cls.list_styles()
+        if ttype != pygments.token.Whitespace
+    ]
+
+
+def builtin_styles():
+    for style_name in pygments.styles.STYLE_MAP:
+        yield (style_name, pygments.styles.get_style_by_name(style_name))
+
+
+def min_contrasts():
+    return {
+        name: min(x[0] for x in get_style_contrasts(style))
+        for name, style in builtin_styles()
+    }
+
+
+def update_json():
+    with open(JSON_FILENAME, "w") as f:
+        json.dump(
+            min_contrasts(),
+            f,
+            indent=2,
+        )
+
+
+def test_contrasts(fail_if_improved=True):
+    with open(JSON_FILENAME) as f:
+        previous_contrasts = json.load(f)
+
+    for style_name in pygments.styles.STYLE_MAP:
+        style = pygments.styles.get_style_by_name(style_name)
+        contrasts = get_style_contrasts(style)
+        min_contrast = min([x[0] for x in contrasts])
+
+        bar = previous_contrasts.get(style_name, WCAG_AA_CONTRAST)
+
+        assert not min_contrast < bar, (
+            "contrast degradation for style '{}'\n"
+            "The following rules have a contrast lower than the required {}:\n\n"
+            "{}\n"
+        ).format(
+            style_name,
+            bar,
+            "\n".join(
+                [
+                    "* {:.2f} {}".format(contrast, ttype)
+                    for contrast, ttype in contrasts
+                    if contrast < bar
+                ]
+            ),
+        )
+
+        if fail_if_improved:
+            assert (
+                not min_contrast > bar
+            ), "congrats, you improved a contrast! please run ./scripts/update_contrasts.py"