First example

ColorToRgb.php

<?php
declare(strict_types=1);

class ColorToRGB
{
    private $color;

    private function __construct(string $color)
    {
        if($this->checkIsValid($color) == true)
            $this->color = $color;
        else
            throw new \InvalidArgumentException("Unsupported Color Name");
    }

    private function checkIsValid(string $color)
    {
        $isValid = false;
        if($color == "black" || $color == "white")
            $isValid = true;

        return $isValid;
    }

    public static function createFromColor(string $color) : self
    {
        return new self($color);
    }

    public function getRGB() : string
    {
        switch ($this->color){
            case "black":
                return "0,0,0";
                break;
            case "white":
                return "255,255,255";
                break;
            default:
                throw new \InvalidArgumentException("Unsupported Color Name");
        }

    }


}

ColorToRGBTest.php

<?php
declare(strict_types=1);

use PHPUnit\Framework\TestCase;

class ColorToRGBTest extends TestCase
{

    /**
     * @dataProvider supportedColorsProvider
     */
    public function testCanBeCreatedForSupportedColors($supportedColor)
    {
        $this->assertInstanceOf(
            ColorToRGB::class,
            ColorToRGB::createFromColor($supportedColor)
            );
    }

    /**
     * @dataProvider unsupportedColorsProvider
     */
    public function testCannotBeCreatedForUnsupportedColors($unsupportedColor)
    {
        $this->expectException(\InvalidArgumentException::class);

        $colorToRgb = ColorToRGB::createFromColor($unsupportedColor);

    }

    /**
     * @dataProvider colorRgbMatchProvider
     */
    public function testGetRgbMatchFromColor($color,$rgbVal)
    {
        $colorToRgb = ColorToRGB::createFromColor($color);
        $this->assertEquals($rgbVal, $colorToRgb->getRGB());
    }

    public function unsupportedColorsProvider()
    {
        return [
            ["red"],
            ["yellow"],
            ["blue"],
            ["green"],
            ["grey"],
            ["purple"],
        ];
    }

    public function supportedColorsProvider()
    {
        return [
            ["black"],
            ["white"]
        ];
    }

    public function colorRgbMatchProvider()
    {
        return [
            ["black","0,0,0"],
            ["white","255,255,255"]
        ];
    }
}