file-system-access/showSaveFilePicker-manual.https.html

<!doctype html>
<meta charset=utf-8>

<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="/resources/testdriver.js"></script>
<script src="/resources/testdriver-vendor.js"></script>
<script src="resources/test-helpers.js"></script>

<script>

  promise_test(async t => {
    await window.test_driver.bless(
      'show a file picker.<br />Please make a copy of file-system-access/resources/data/testfile.txt in a writable directory and pick that file');
    const file = await self.showSaveFilePicker({
      multiple: false, types: [
        { description: 'Text files', accept: { 'text/plain': ['.txt'] } },
      ],
    });
    assert_true(file instanceof FileSystemHandle);
    assert_true(file instanceof FileSystemFileHandle);
    assert_equals(file.kind, "file");
    assert_equals(file.name, 'testfile.txt');
    assert_equals(await (await file.getFile()).text(), '',
      'showSaveFilePicker should clear contents of file');

    promise_test(async t => {
      assert_equals(await file.queryPermission(), 'granted');
      assert_equals(await file.queryPermission({ mode: 'readwrite' }), 'granted');
    }, 'showSaveFilePicker returns correct permissions');
  }, 'showSaveFilePicker works');

</script>