testColorDiff() {
    const colors = {
      'mediumblue': [0, 0, 205],
      'oldlace': [253, 245, 230],
      'orchid': [218, 112, 214],
    };

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

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

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

    // color diff for known pairs should match known values
    assertEquals(
        'mediumblue-oldlace is 523.', diffs['mediumblue-oldlace'], 523);
    assertEquals('oldlace-orchid is 184.', diffs['oldlace-orchid'], 184);

    // reversed pairs should have equal values
    assertEquals('orchid-mediumblue is 339.', diffs['orchid-mediumblue'], 339);
    assertEquals(
        'mediumblue-orchid is also 339.', diffs['mediumblue-orchid'], 339);
  }
This method runs unit tests against googColor.colorDiff_().
@suppress {visibility} accessing private properties