Recommended way to mock Kingfisher in tests?

[CraigSiemens]

I'm trying to write some tests for a view in the app that contains an image that's loaded by Kingfisher. I have a couple options for the type of tests I could write, but I'm not finding a obvious way to mock out Kingfisher for use in tests.

If I write a unit test, I can create a subclass of ImageDownloader and override downloadImage to check if it's passed the correct values. But I can't then manually call the completion with a mock image since ImageLoadingResult doesn't have a public init.

If I write a snapshot test, I can pass it a file url but that is asynchronously loaded after the snapshot is taken. Subclassing ImageDownloader to synchronously return an image also isn't an option since the result also doesn't have a public init.

[onevcat]

I am not quite sure what kind of test you are trying to add, or say, can you paste some pseudo-code so we can have a more concrete context to discuss.

If I write a snapshot test, I can pass it a file url but that is asynchronously loaded after the snapshot is taken

If a file URL is an option for your testing, then maybe this load​Disk​File​Synchronously can help you out:

KF.url(fileURL)
  .loadDiskFileSynchronously()
  .set(to: imageView)

// Or if you prefer the image view extension:
imageView.kf.setImage(with: fileURL, options: [.loadDiskFileSynchronously])

[CraigSiemens]

We're using https://github.com/pointfreeco/swift-snapshot-testing to take snapshots of our views in some of our tests. The goal was to have two tests, one to make sure the view had the correct appearance when the image hadn't loaded yet, and another for after the image did load.

What I ended up doing is making a cache in the test and setting the default options on kingfisher to to only use that cache. Something like this.

describe("appearance") {
    beforeEach {
        imageCache = ImageCache(name: self.name)
	
        KingfisherManager.shared.defaultOptions = [
            .onlyFromCache,
            .targetCache(imageCache)
        ]
    }

    afterEach {
        KingfisherManager.shared.defaultOptions = []
    }

    context("when the image hasn't loaded yet") {
        beforeEach {
            imageCache.clearMemoryCache()
            view.configure(with: viewModel)
        }
        
        it("should have a dark background") {
            expect(view).to(haveMatchingSnapshot())
        }
    }

    context("when the image has loaded") {
        beforeEach {
            imageCache.store(
                .placeholder,
                forKey: expectedURL.cacheKey,
                toDisk: false
            )
	    
            view.configure(with: viewModel)
        }
        
        it("should show the image") {
            expect(view).to(haveMatchingSnapshot())
        }
    }
}

[tylerlantern]

Update

    let cache = ImageCache(name: "VoucherDetailComponentTests")
    KingfisherManager.shared.defaultOptions = [
      .onlyFromCache,
      .targetCache(cache)
    ]
    let options : [KingfisherOptionsInfoItem] = [.targetCache(cache)]
     cache.store(
       KFCrossPlatformImage(systemName: "fireplace.fill")!,
       forKey:  Notify.Voucher.Place.mock.logo!.cacheKey,
       options: KingfisherParsedOptionsInfo(KingfisherOptionsInfo(options))
     )

where Notify.Voucher.Place.mock.logo is URL Type
I used snapshot testing from ttps://github.com/pointfreeco/swift-snapshot-testing to test image

[MartinStrambach]

FYI this approach was broken by #2036 in 7.6.2 if you use startLoadingBeforeViewAppear