function assertIdpButtonLabels(button, expectedShortLabel, expectedLongLabel) {
  const idpTextLong = dom.getElementsByClass(
    'firebaseui-idp-text-long', button);
  const idpTextShort = dom.getElementsByClass(
    'firebaseui-idp-text-short', button);

  assertEquals(
      expectedLongLabel,
      dom.getTextContent(idpTextLong[0]));
  assertEquals(
      expectedShortLabel,
      dom.getTextContent(idpTextShort[0]));
}
Asserts the IdP or tenant button has correct labels.
@param {!Element} button The IdP or tenant button.
@param {string} expectedShortLabel The expected short label of the button.
@param {string} expectedLongLabel The expected long label of the button.