LayoutTests/cssom/array-concat-adoptedStyleSheets.html

<!DOCTYPE html>
<html>
<body>
<script src="../resources/js-test.js"></script>
<script>
description("Tests that Array.concat() behaves correctly with an observable array returned by adoptedStyleSheets.");

let a = new CSSStyleSheet;
let b = new CSSStyleSheet;
let c = new CSSStyleSheet;
document.adoptedStyleSheets.push(b);
document.adoptedStyleSheets.push(c);
shouldBe("document.adoptedStyleSheets.length", "2");

let newArray = [a].concat(document.adoptedStyleSheets);
shouldBe("newArray.length", "3");
shouldBe("document.adoptedStyleSheets.length", "2");
shouldBe("newArray[0]", "a");
shouldBe("newArray[1]", "b");
shouldBe("newArray[2]", "c");
</script>
</body>
</html>