Added a high contrast mode to screenshot cases.

Thank you to Sarah Abderemane and Nick Pope for the reviews.

django/test/selenium.py

@@ -191,6 +191,26 @@ def dark(self):
             finally:
                 self.selenium.execute_script("localStorage.removeItem('theme');")
 
+    def set_emulated_media(self, features, media=""):
+        if self.browser != "chrome":
+            self.skipTest("Emulated media controls are only supported on Chrome.")
+        # Chrome Dev Tools Protocol Emulation.setEmulatedMedia
+        # https://chromedevtools.github.io/devtools-protocol/1-3/Emulation/#method-setEmulatedMedia
+        self.selenium.execute_cdp_cmd(
+            "Emulation.setEmulatedMedia", {"media": media, "features": features}
+        )
+
+    @contextmanager
+    def high_contrast(self):
+        self.set_emulated_media(features=[{"name": "forced-colors", "value": "active"}])
+        with self.desktop_size():
+            try:
+                yield
+            finally:
+                self.set_emulated_media(
+                    features=[{"name": "forced-colors", "value": "none"}]
+                )
+
     def take_screenshot(self, name):
         if not self.screenshots:
             return

docs/internals/contributing/writing-code/unit-tests.txt

@@ -278,24 +278,25 @@ For testing changes to the admin UI, the selenium tests can be run with the
 To define when screenshots should be taken during a selenium test, the test
 class must use the ``@django.test.selenium.screenshot_cases`` decorator with a
 list of supported screenshot types (``"desktop_size"``, ``"mobile_size"``,
-``"small_screen_size"``, ``"rtl"``, and ``"dark"``). It can then call
-``self.take_screenshot("unique-screenshot-name")`` at the desired point to
-generate the screenshots. For example::
+``"small_screen_size"``, ``"rtl"``, ``"dark"``, and ``"high_contrast"``). It
+can then call ``self.take_screenshot("unique-screenshot-name")`` at the desired
+point to generate the screenshots. For example::
 
     from django.test.selenium import SeleniumTestCase, screenshot_cases
     from django.urls import reverse
 
 
     class SeleniumTests(SeleniumTestCase):
-        @screenshot_cases(["desktop_size", "mobile_size", "rtl", "dark"])
+        @screenshot_cases(["desktop_size", "mobile_size", "rtl", "dark", "high_contrast"])
         def test_login_button_centered(self):
             self.selenium.get(self.live_server_url + reverse("admin:login"))
             self.take_screenshot("login")
             ...
 
 This generates multiple screenshots of the login page - one for a desktop
 screen, one for a mobile screen, one for right-to-left languages on desktop,
-and one for the dark mode on desktop.
+one for the dark mode on desktop, and one for high contrast mode on desktop
+when using chrome.
 
 .. versionchanged:: 5.1
 

tests/admin_views/tests.py

@@ -5764,7 +5764,7 @@ def setUp(self):
             title="A Long Title", published=True, slug="a-long-title"
         )
 
-    @screenshot_cases(["desktop_size", "mobile_size", "rtl", "dark"])
+    @screenshot_cases(["desktop_size", "mobile_size", "rtl", "dark", "high_contrast"])
     def test_login_button_centered(self):
         from selenium.webdriver.common.by import By
 
@@ -6070,7 +6070,7 @@ def test_populate_existing_object(self):
         self.assertEqual(slug1, "this-is-the-main-name-the-best-2012-02-18")
         self.assertEqual(slug2, "option-two-this-is-the-main-name-the-best")
 
-    @screenshot_cases(["desktop_size", "mobile_size", "dark"])
+    @screenshot_cases(["desktop_size", "mobile_size", "dark", "high_contrast"])
     def test_collapsible_fieldset(self):
         """
         The 'collapse' class in fieldsets definition allows to
@@ -6093,7 +6093,7 @@ def test_collapsible_fieldset(self):
         )
         self.take_screenshot("expanded")
 
-    @screenshot_cases(["desktop_size", "mobile_size", "rtl", "dark"])
+    @screenshot_cases(["desktop_size", "mobile_size", "rtl", "dark", "high_contrast"])
     def test_selectbox_height_collapsible_fieldset(self):
         from selenium.webdriver.common.by import By
 
@@ -6121,7 +6121,7 @@ def test_selectbox_height_collapsible_fieldset(self):
         )
         self.take_screenshot("selectbox-collapsible")
 
-    @screenshot_cases(["desktop_size", "mobile_size", "rtl", "dark"])
+    @screenshot_cases(["desktop_size", "mobile_size", "rtl", "dark", "high_contrast"])
     def test_selectbox_height_not_collapsible_fieldset(self):
         from selenium.webdriver.common.by import By
 
@@ -6152,7 +6152,7 @@ def test_selectbox_height_not_collapsible_fieldset(self):
         )
         self.take_screenshot("selectbox-non-collapsible")
 
-    @screenshot_cases(["desktop_size", "mobile_size", "rtl", "dark"])
+    @screenshot_cases(["desktop_size", "mobile_size", "rtl", "dark", "high_contrast"])
     def test_first_field_focus(self):
         """JavaScript-assisted auto-focus on first usable form field."""
         from selenium.webdriver.common.by import By