testHslDistance() {
    // Define some HSL colors
    const aliceBlueHsl = googColor.rgbToHsl(240, 248, 255);
    const blackHsl = googColor.rgbToHsl(0, 0, 0);
    const ghostWhiteHsl = googColor.rgbToHsl(248, 248, 255);
    const navyHsl = googColor.rgbToHsl(0, 0, 128);
    const redHsl = googColor.rgbToHsl(255, 0, 0);
    const whiteHsl = googColor.rgbToHsl(255, 255, 255);

    // The distance between the same colors should be 0.
    assertTrue(
        'There is no HSL distance between white and white.',
        googColor.hslDistance(whiteHsl, whiteHsl) == 0);
    assertTrue(
        'There is no HSL distance between red and red.',
        googColor.hslDistance(redHsl, redHsl) == 0);

    // The distance between various colors should be within certain thresholds.
    let hslDistance = googColor.hslDistance(whiteHsl, ghostWhiteHsl);
    assertTrue(
        'The HSL distance between white and ghost white is > 0.',
        hslDistance > 0);
    assertTrue(
        'The HSL distance between white and ghost white is <= 0.02.',
        hslDistance <= 0.02);
    hslDistance = googColor.hslDistance(whiteHsl, redHsl);
    assertTrue(
        'The HSL distance between white and red is > 0.02.',
        hslDistance > 0.02);
    hslDistance = googColor.hslDistance(navyHsl, aliceBlueHsl);
    assertTrue(
        'The HSL distance between navy and alice blue is > 0.02.',
        hslDistance > 0.02);
    hslDistance = googColor.hslDistance(blackHsl, whiteHsl);
    assertTrue(
        'The HSL distance between white and black is 1.', hslDistance == 1);
  }
This method runs unit tests against googColor.hslDistance().