css/cssom/cssimportrule-sheet-identity.html

<!doctype html>
<title>CSSImportRule has different sheets even if referencing the same URL</title>
<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<link rel="help" href="https://drafts.csswg.org/cssom/#the-cssimportrule-interface">
<link rel="stylesheet" href="support/import-rule.css">
<link rel="stylesheet" href="support/import-rule.css">
<script>
let t = async_test("CSSImportRule has different sheets even if referencing the same URL");
window.onload = t.step_func_done(function() {
  let sheet1 = document.styleSheets[0];
  let sheet2 = document.styleSheets[1];

  assert_not_equals(sheet1, sheet2);

  let childSheet1 = sheet1.cssRules[0].styleSheet;
  let childSheet2 = sheet2.cssRules[0].styleSheet;

  assert_not_equals(childSheet1, null);
  assert_not_equals(childSheet2, null);
  assert_not_equals(childSheet1, childSheet2, "@import pointing to the same URL shouldn't point to the same StyleSheet object");
});
</script>