chrome/test/data/extensions/api_test/system/get_incognito_mode_availability/test.html

<script>
// System API test
// Run with browser_tests --gtest_filter=ExtensionApiTest.GetIncognitoModeAvailability

function expect(expected, message) {
  return chrome.test.callbackPass(function(value) {
    chrome.test.assertEq(expected, value, message);
  });
}

chrome.test.runTests([
  function getIncognitoModeAvailabilityTest() {
    chrome.systemPrivate.getIncognitoModeAvailability(expect(
        'disabled',
        "Pref `chrome.system.getIncognitoModeAvailability` is expected to " +
        "return 'disabled'"));
  },
]);
</script>