testYiqBrightnessDiff() {
    const colors = {
      'deeppink': [255, 20, 147],
      'indigo': [75, 0, 130],
      'saddlebrown': [139, 69, 19],
    };

    const diffs = new Object();
    for (let name1 in colors) {
      for (let name2 in colors) {
        diffs[`${name1}-${name2}`] =
            googColor.yiqBrightnessDiff_(colors[name1], colors[name2]);
      }
    }

    for (let pair in diffs) {
      // each brightness diff should be a number
      assertTrue(`${pair} diff is a number.`, typeof diffs[pair] == 'number');
      // each brightness diff should be greater than or equal to 0
      assertTrue(
          `${pair} diff is greater than or equal to 0.`, diffs[pair] >= 0);
    }

    // brightness diff for same-color pairs should be 0
    assertEquals('deeppink-deeppink is 0.', diffs['deeppink-deeppink'], 0);
    assertEquals('indigo-indigo is 0.', diffs['indigo-indigo'], 0);

    // brightness diff for known pairs should match known values
    assertEquals('deeppink-indigo is 68.', diffs['deeppink-indigo'], 68);
    assertEquals(
        'saddlebrown-deeppink is 21.', diffs['saddlebrown-deeppink'], 21);

    // reversed pairs should have equal values
    assertEquals('indigo-saddlebrown is 47.', diffs['indigo-saddlebrown'], 47);
    assertEquals(
        'saddlebrown-indigo is also 47.', diffs['saddlebrown-indigo'], 47);
  }
This method runs unit tests against googColor.yiqBrightnessDiff_().
@suppress {visibility} accessing private properties