 sheet.deleteRule(0);
      assert_equals(cssRules.length, 0, 'Sheet should have no rule');
    }, rule + ' should still be a valid import rule with an invalid supports() declaration');
  }

  function test_invalid_supports_import(rule) {
    test(function() {
      const style = document.createElement("style");
      document.head.append(style);
      const {sheet} = style;
      const {cssRules} = sheet;

      assert_equals(cssRules.length, 0, "Sheet should have no rules");
    }, rule + ' should be an i