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Test Info:

<!DOCTYPE HTML>
<html>
<!--
-->
<head>
<meta charset="utf-8">
<title>Test for Bug 1691793</title>
<script src="/tests/SimpleTest/SimpleTest.js"></script>
<link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
</head>
<body>
<p id="display"></p>
<div id="content" style="display: none">
</div>
<pre id="test">
</pre>
<script>
"use strict";
SimpleTest.registerCleanupFunction(async () => {
await SpecialPowers.flushPrefEnv();
});
// Returns a Promise which will be resolved when the "change" event is received
// for the given media query string.
function promiseForChange(mediaQuery) {
return new Promise(resolve => {
window.matchMedia(mediaQuery).addEventListener("change", event => {
resolve(event.matches);
}, { once: true });
});
}
add_task(async () => {
await SpecialPowers.pushPrefEnv({ set: [["layout.css.prefers-contrast.enabled", true]]});
const initiallyMatches =
window.matchMedia("(prefers-contrast: more)").matches;
const changePromise = initiallyMatches ?
promiseForChange("(prefers-contrast: more)") : null;
await SpecialPowers.pushPrefEnv({ set: [["ui.useAccessibilityTheme", 0]]});
if (changePromise) {
await changePromise;
}
ok(!window.matchMedia("(prefers-contrast: more)").matches,
"Does not match prefers-contrast: more) when the system unsets " +
"UseAccessibilityTheme");
ok(!window.matchMedia("(prefers-contrast)").matches,
"Does not match (prefers-contrast) when the system unsets " +
"UseAccessibilityTheme");
ok(window.matchMedia("(prefers-contrast: no-preference)").matches,
"Matches (prefers-contrast: no-preference) when the system unsets " +
"UseAccessibilityTheme");
});
add_task(async () => {
const more = promiseForChange("(prefers-contrast: more)");
const booleanContext = promiseForChange("(prefers-contrast)");
const noPreference = promiseForChange("(prefers-contrast: no-preference)");
await SpecialPowers.pushPrefEnv({ set: [["ui.useAccessibilityTheme", 1]]});
const [ moreResult, booleanContextResult, noPreferenceResult ] =
await Promise.all([ more, booleanContext, noPreference ]);
ok(moreResult,
"Matches (prefers-contrast: more) when the system sets " +
"UseAccessibilityTheme");
ok(booleanContextResult,
"Matches (prefers-contrast) when the system sets UseAccessibilityTheme");
ok(!noPreferenceResult,
"Does not match (prefers-contrast: no-preference) when the " +
"system sets UseAccessibilityTheme");
});
</script>
</body>
</html>