Add string render test

src/SDLFontAtlas.cake

@@ -334,6 +334,27 @@
        20 100 "The quick brown fox\n
  jumps over the lazy dog.")
 
+      (scope
+       (var string-bounds SDL_Rect (array 0))
+       (var test-str (addr (const char)) " hel o   ")
+       (get-string-render-size
+        (addr atlas)
+        test-str (strlen test-str)
+        (addr (field string-bounds x)) (addr (field string-bounds y))
+        (addr (field string-bounds w)) (addr (field string-bounds h)))
+       (set-fields string-bounds
+         w (- (field string-bounds w) (field string-bounds x))
+         h (- (field string-bounds h) (field string-bounds y))
+         x (+ (field string-bounds x) 100)
+         y (+ (field string-bounds y) 200))
+       (SDL_SetRenderDrawColor
+        renderer 255 255 255 255)
+       (SDL_RenderDrawRect renderer (addr string-bounds))
+       (render-string-length renderer (addr atlas)
+                             texture
+                             100 200
+                             test-str (strlen test-str)))
+
       (SDL_RenderPresent renderer)
       (SDL_UpdateWindowSurface window))