Add tests for PR #505 with RGB to HSL fix

[mloskot]

Contributor of #505 posted GTest-based tests in https://github.com/boostorg/gil/pull/505#issuecomment-653915440, copied below. We need to port this to Boost.LightweightTest

#define rgb2hsl(r, g, b, h, s, l)                              \
  {                                                            \
    const float abs_error = 0.002;                             \
    using boost::gil::hsl32f_pixel_t;                          \
    using boost::gil::rgb8_pixel_t;                            \
    using boost::gil::hsl_color_space::hue_t;                  \
    using boost::gil::hsl_color_space::lightness_t;            \
    using boost::gil::hsl_color_space::saturation_t;           \
    rgb8_pixel_t rgb(r, g, b);                                 \
    hsl32f_pixel_t hsl;                                        \
                                                               \
    color_convert(rgb, hsl);                                   \
                                                               \
    ASSERT_NEAR(h, get_color(hsl, hue_t()), abs_error);        \
    ASSERT_NEAR(s, get_color(hsl, saturation_t()), abs_error); \
    ASSERT_NEAR(l, get_color(hsl, lightness_t()), abs_error);  \
  }

#define hsl2rgb(h, s, l, r, g, b)                         \
  {                                                       \
    const float abs_error = 1;                            \
    using boost::gil::blue_t;                             \
    using boost::gil::green_t;                            \
    using boost::gil::hsl32f_pixel_t;                     \
    using boost::gil::red_t;                              \
    using boost::gil::rgb8_pixel_t;                       \
    hsl32f_pixel_t hsl(h, s, l);                          \
    rgb8_pixel_t rgb;                                     \
                                                          \
    color_convert(hsl, rgb);                              \
                                                          \
    ASSERT_NEAR(r, get_color(rgb, red_t()), abs_error);   \
    ASSERT_NEAR(g, get_color(rgb, green_t()), abs_error); \
    ASSERT_NEAR(b, get_color(rgb, blue_t()), abs_error);  \
  }

TEST(ColorSpaceTest, RGBToHSL) {
  // black
  rgb2hsl(0, 0, 0, 0, 0, 0);

  // white
  rgb2hsl(255, 255, 255, 0, 0, 1);

  // red
  rgb2hsl(255, 0, 0, 0, 1, 0.5);

  // lime
  rgb2hsl(0, 255, 0, 2 / 6.f, 1, 0.5);

  // blue
  rgb2hsl(0, 0, 255, 4 / 6.f, 1, 0.5);

  // yellow
  rgb2hsl(255, 255, 0, 1 / 6.f, 1, 0.5);

  // cyan
  rgb2hsl(0, 255, 255, 3 / 6.f, 1, 0.5);

  // magenta
  rgb2hsl(255, 0, 255, 5 / 6.f, 1, 0.5);

  // silver
  rgb2hsl(191, 191, 191, 0, 0, 0.75);

  // gray
  rgb2hsl(128, 128, 128, 0, 0, 0.5);

  // maroon
  rgb2hsl(128, 0, 0, 0, 1, 0.25);

  // olive
  rgb2hsl(128, 128, 0, 1 / 6.f, 1, 0.25);

  // green
  rgb2hsl(0, 128, 0, 2 / 6.f, 1, 0.25);

  // purple
  rgb2hsl(128, 0, 128, 5 / 6.f, 1, 0.25);

  // teal
  rgb2hsl(0, 128, 128, 3 / 6.f, 1, 0.25);

  // navy
  rgb2hsl(0, 0, 128, 4 / 6.f, 1, 0.25);
}

TEST(ColorSpaceTest, HSLToRGB) {
  // black
  hsl2rgb(0, 0, 0, 0, 0, 0);

  // white
  hsl2rgb(0, 0, 1, 255, 255, 255);

  // red
  hsl2rgb(0, 1, 0.5, 255, 0, 0);

  // lime
  hsl2rgb(2 / 6.f, 1, 0.5, 0, 255, 0);

  // blue
  hsl2rgb(4 / 6.f, 1, 0.5, 0, 0, 255);

  // purple
  hsl2rgb(5 / 6.f, 1, 0.25, 128, 0, 128);

  // teal
  hsl2rgb(3 / 6.f, 1, 0.25, 0, 128, 128);

  // navy
  hsl2rgb(4 / 6.f, 1, 0.25, 0, 0, 128);
}