service-worker: improving a test so that postMessage is taken into account (ref. #8)

__tests__/service-worker.test.js

@@ -422,13 +422,26 @@ describe("service-worker", () => {
         fetch: resolvingFetch2
     })
     
+    var testClient = new Client()
+    self.clients.clients.push(testClient)
+    var fetchedDiffersFound = false
+    testClient.addEventListener('message', event => {
+      if (event.data.fetchedDiffers) {
+        fetchedDiffersFound = true
+      }
+    })
+    
     require("../service-worker.js");
     
-    var response = await self.trigger('fetch', new Request('/test.json'))
+    var response = await self.trigger('fetch', {
+      request: new Request('/test.json'),
+      clientId: testClient.id
+    })
     expect(resolvingFetch).toHaveBeenCalled();
     expect(await response.json()).toEqual({ test: "success" })
     expect(resolvingFetch2).toHaveBeenCalled();
     expect(stashingStash).toHaveBeenCalled();
+    expect(fetchedDiffersFound).toEqual(true)
   });
   
   test("content should be stashed if it was retrieved from a job after retrieval from a stashing plugin, even it does not differ from the stashed version", async () => {