Contao\CoreBundle\Test\Contao\GdImageTest::testConvertToPaletteImageFromTrueColor PHP Method

    public function testConvertToPaletteImageFromTrueColor()
    {
        $image = imagecreatetruecolor(100, 100);
        for ($x = 0; $x < 100; ++$x) {
            for ($y = 0; $y < 100; ++$y) {
                imagefilledrectangle($image, $x, $y, $x + 1, $y + 1, imagecolorallocatealpha($image, $x, $y, 0, 0));
            }
        }
        // Bottom right pixel transparent
        imagealphablending($image, false);
        imagefilledrectangle($image, 99, 99, 100, 100, imagecolorallocatealpha($image, 0, 0, 0, 127));
        $image = new GdImage($image);
        $image->convertToPaletteImage();
        $this->assertInternalType('resource', $image->getResource());
        $this->assertFalse(imageistruecolor($image->getResource()));
        $this->assertEquals(256, imagecolorstotal($image->getResource()));
        $this->assertEquals(127, imagecolorsforindex($image->getResource(), imagecolorat($image->getResource(), 99, 99))['alpha'], 'Bottom right pixel should be transparent');
    }