Add GD-specific tests

Test: gd

scripts/tests/gd.php

@@ -0,0 +1,69 @@
+<?php
+
+$imageWidth = 8;
+$imageHeight = 16;
+$image = imagecreatetruecolor($imageWidth, $imageHeight);
+$formats = array(
+    'gd2',
+    'gif',
+    'jpeg',
+    'png',
+    'wbmp',
+    'webp',
+    'wbmp',
+    'xbm',
+    'xpm',
+    'gd',
+);
+if (PHP_VERSION_ID >= 70200) {
+    $formats = array_merge($formats, array(
+        'bmp',
+    ));
+}
+$tempFile = null;
+$image2 = null;
+try {
+    foreach ($formats as $format) {
+        $loadFuntion = "imagecreatefrom${format}";
+        if (!function_exists($loadFuntion)) {
+            throw new Exception("$loadFuntion() function is missing");
+        }
+        if ($format === 'xpm') {
+            continue;
+        }
+        $saveFuntion = "image${format}";
+        if (!function_exists($saveFuntion)) {
+            throw new Exception("$saveFuntion() function is missing");
+        }
+        $tempFile = tempnam(sys_get_temp_dir(), 'dpei');
+        if ($saveFuntion($image, $tempFile) === false) {
+            throw new Exception("$saveFuntion() failed");
+        }
+        if (!is_file($tempFile) || filesize($tempFile) < 1) {
+            throw new Exception("$saveFuntion() created an empty file");
+        }
+        $image2 = $loadFuntion($tempFile);
+        unlink($tempFile);
+        $tempFile = null;
+        if (!is_resource($image2) || imagesx($image2) !== $imageWidth || imagesy($image2) !== $imageHeight) {
+            throw new Exception("$loadFuntion() failed");
+        }
+        imagedestroy($image2);
+    }
+} finally {
+    imagedestroy($image);
+    if (is_resource($image2)) {
+        imagedestroy($image2);
+    }
+    if($tempFile !== null) {
+        unlink($tempFile);
+    }
+}
+
+if (!function_exists('imagefttext')) {
+    throw new Exception("imagefttext() function is missing");    
+}
+if (!function_exists('imageantialias')) {
+    throw new Exception("imageantialias() function is missing");    
+}
+return true;