chromium/third_party/blink/web_tests/fast/css/opacity-float.html

<script>
if (window.testRunner) {
    testRunner.dumpAsText();

    // Put ourselves in a locale where 0.9 is written as "0,9".
    testRunner.setPOSIXLocale("pl_PL.UTF-8");
}
</script>

<p>This test verifies that reading a floating-point opacity from CSS
attributes gets back a properly-formatted float.  Improperly handling
locales that cause decimals to be written as commas might break
it.</p>

<a id='test' style='opacity:.9'></a>

<script>
var opacity = document.getElementById('test').style.opacity.toString();
if (opacity == '0.9')
    document.write('PASS');
else
    document.write('FAIL: ' + opacity);

if (window.testRunner) {
    // Put ourselves back(?) in a locale where 0.9 is written as "0.9".
    testRunner.setPOSIXLocale("C");
}
</script>