How to test this function using Jest

[sharp apex]

I have the following function which aims to resize a requested image to the desired resolution. If the image was already resized and it's cached, it is sent directly from the redis cache. Example scenario: GET request to http://www.resize.com/image1.jpg?resolution=1920x1080 . If it was not cached, image1.jpg will be resized to 1920x1080 and sent back. I am struggling to make an appropriate jest test and also mock sharp and redis client. Thank you!

[pine junco]

processImage()

• Returns image if already cached:
  • Ensure the returned image is the same as expected.
  • Ensure the number of cacheHits is incremented.
  • Ensure the returned image is in the correct format.
• Loads and processes the image:
  • Ensure the image has been cached under cacheKey.
  • Ensure the number of cacheMisses is incremented.
  • Ensure the imagesResizedCount is increased.
  • Ensure the returned image is in the correct format.
• Resizes the image if a resolution is passed before returning:
  • Ensure the returned image is of the correct size.

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Your function could be broken up into 2-3 smaller functions, you'd find it easier and more approachable to test them.