Use LAB hopper file if conversion is not supported

Author: radarhere

Tests/helper.py

@@ -273,7 +273,14 @@ def _cached_hopper(mode: str) -> Image.Image:
  im = hopper("L")
  else:
  im = hopper()
- return im.convert(mode)
+ try:
+ im = im.convert(mode)
+ except ImportError:
+ if mode == "LAB":
+ im = Image.open("Tests/images/hopper.Lab.tif")
+ else:
+ raise
+ return im
 
 
 def djpeg_available() -> bool: