ThreadSafetyTests: add failing test where we load and store an image

[AndrewSB]

adds a test that shows #750

[kean]

Hey @AndrewSB, thanks for providing the sample code. I now realized what I was missing, and it was pretty obvious.

The default pipeline (ImagePipeline.shared) does not use Nuke.DataCache but instead relies on the Foundation.URLCache. Unfortunately, the following APIs only with the custom caches added by Nuke and not the caches that are part of the data loading system:

ImagePipeline.shared.cache.storeCachedData(imageData, for: ImageRequest(url: remoteURL)

In order to make this test pass, you need to do the following:

// 1. Enable custom disk cache
let pipeline = ImagePipeline(configuration: .withDataCache)

// 2. Use real image data, otherwise the cached data gets ignored
let imageData = try XCTUnwrap(Test.data(name: "fixture", extension: "jpeg"))

With these two changes, you get the following response:

    ▿ cacheType : Optional<CacheType>
      - some : Nuke.ImageResponse.CacheType.disk

Caching is one of the more compiled aspects in any image loading framework, so I would recommend going through the related documentation.

[kean]

Thanks for updating the test. I'm going to merge and update it a bit – it shouldn't use the default cache.

[AndrewSB]

that makes sense! i wrote it that way because that's how i'm using it in my project, i assumed you'd want on which is created inline. appreciate the help @kean!