In multi_resize() image editor methods, assert that null can only be passed for one of the arguments, not both. Add a lot more unit test assertions to ensure this.

Props pbearne, DH-Shredder.
Fixes #26823.



git-svn-id: https://develop.svn.wordpress.org/trunk@27794 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/class-wp-image-editor.php

@@ -82,13 +82,17 @@ abstract class WP_Image_Editor {
 	/**
 	 * Resizes current image.
 	 *
+	 * At minimum, either a height or width must be provided.
+	 * If one of the two is set to null, the resize will
+	 * maintain aspect ratio according to the provided dimension.
+	 *
 	 * @since 3.5.0
 	 * @access public
 	 * @abstract
 	 *
-	 * @param int $max_w
-	 * @param int $max_h
-	 * @param boolean $crop
+	 * @param  int|null $max_w Image width.
+	 * @param  int|null $max_h Image height.
+	 * @param  boolean  $crop
 	 * @return boolean|WP_Error
 	 */
 	abstract public function resize( $max_w, $max_h, $crop = false );