qual: add test assertions on image sizes

Expected to fail because in the current implementation,
Image::fromString() calculates the image size but
methods like PNG::fromString() and JPEG::fromFile()
don't.

tests/Format/JPEGTest.php

@@ -49,6 +49,9 @@ public function testGetXmp($method, $filename, $expectedHeadline)
             throw new \InvalidArgumentException("Invalid method: $method");
         }
 
+        $this->assertInstanceOf(JPEG::class, $jpeg);
+        $this->assertGreaterThan(0, $jpeg->getSize()["width"]);
+
         $xmp = $jpeg->getXmp();
 
         $this->assertInstanceOf(Xmp::class, $xmp);

tests/Format/PNGTest.php

@@ -51,6 +51,9 @@ public function testGetXmp($method, $filename, $expectedPhotographerName, $expec
             throw new \InvalidArgumentException("Invalid method: $method");
         }
 
+        $this->assertInstanceOf(PNG::class, $png);
+        $this->assertGreaterThan(0, $png->getSize()["width"]);
+
         $xmp = $png->getXmp();
 
         $this->assertInstanceOf(Xmp::class, $xmp);

tests/Format/WebPTest.php

@@ -49,6 +49,7 @@ public function testValidWebP($method, $filename, $expectedHeadline)
         }
 
         $this->assertInstanceOf(WebP::class, $webp);
+        $this->assertGreaterThan(0, $webp->getSize()["width"]);
 
         $xmp = $webp->getXmp();