Makes an image use grayscale.
Inheritance: implements Liip\ImagineBundle\Imagine\Filter\Loader\LoaderInterface
 public function testLoad()
 {
     $image = $this->getMock('\\Imagine\\Image\\ImageInterface');
     $effects = $this->getMock('\\Imagine\\Effects\\EffectsInterface');
     $image->expects($this->once())->method('effects')->will($this->returnValue($effects));
     $effects->expects($this->once())->method('grayscale')->will($this->returnValue($effects));
     $loader = new GrayscaleFilterLoader();
     $this->assertSame($image, $loader->load($image));
 }