This is a testharness.js-based test.
[FAIL] new ClipboardItem() fails for custom formats with web prefix, but invalid MIME types
  assert_throws_js: function "() => {\n    const clipboardItemInput = new ClipboardItem(\n    {[format1]: blobInput1, [format2]: blobInput2});\n  }" did not throw
Harness: the test ran to completion.