     let image = helper.image
     let key = #function
 
-    waitUntil { done in
+    waitUntil(timeout: 5) { done in
       cache.store(image, forKey: key) {
         cache.clearMemory()
         cache.clearDisk {

    let image = helper.image
    let key = "http://\(#function)"
    
    waitUntil { done in
      cache.store(image, forKey: key) {
        cache.retrieveImage(forKey: key) { image, type in
          expect(image).toNot(beNil())

final class CacheTests: XCTestCase {
  
  private let helper = TestHelper()
  
  class MockStore: BackingStore {
    
