testColorLighten() {
    // Define some RGB colors
    const black = [0, 0, 0];
    const brown = [165, 42, 42];
    const navy = [0, 0, 128];
    const orange = [255, 165, 0];
    const white = [255, 255, 255];

    // Lighten white by an arbitrary factor, which should still return white.
    const lightWhite = googColor.lighten(white, .41);
    assertTrue(
        'white lightened by .41 is still white.',
        rgbColorsAreEqual(white, lightWhite));

    // Call lighten() with edge-case factors(0 and 1).
    const navyNotLightened = googColor.lighten(navy, 0);
    assertTrue(
        'navy lightened by 0 is still navy.',
        rgbColorsAreEqual(navy, navyNotLightened));
    const orangeFullyLightened = googColor.lighten(orange, 1);
    assertTrue(
        'orange lightened by 1 is white.',
        rgbColorsAreEqual(white, orangeFullyLightened));

    // Call lighten() with various colors and factors. The result should be
    // a color with greater luminance.
    const blackHsl = googColor.rgbToHsl(black[0], black[1], black[2]);
    const blackLightened = googColor.lighten(black, .33);
    const blackLightenedHsl = googColor.rgbToHsl(
        blackLightened[0], blackLightened[1], blackLightened[2]);
    assertTrue(
        'Black that\'s lightened has more luminance than black.',
        blackLightenedHsl[2] >= blackHsl[2]);
    const orangeHsl = googColor.rgbToHsl(orange[0], orange[1], orange[2]);
    const orangeLightened = googColor.lighten(orange, .91);
    const orangeLightenedHsl = googColor.rgbToHsl(
        orangeLightened[0], orangeLightened[1], orangeLightened[2]);
    assertTrue(
        'Orange that\'s lightened has more luminance than orange.',
        orangeLightenedHsl[2] >= orangeHsl[2]);

    // Call lighten() with factors outside the expected range.
    const navyTurnedWhite = googColor.lighten(navy, 1.01);
    assertTrue(
        'Lightening navy by 1.01 returns white.',
        rgbColorsAreEqual(white, navyTurnedWhite));
    const brownNotLightened = googColor.lighten(brown, -0.0000001);
    assertTrue(
        'Lightening brown by -0.0000001 returns brown.',
        rgbColorsAreEqual(brown, brownNotLightened));
  }
This method runs unit tests against googColor.lighten(). Test cases
include lightening white with arbitrary factors, edge cases (using 0 and
1), lightening colors using various factors, and lightening colors using
factors outside the expected range.