Remove handling of duplicate storage diffs in watcher

- Can push this responsibility down to the transformers
- Update docs to reflect that transformers should handle duplicates

libraries/shared/watcher/storage_watcher.go

@@ -78,7 +78,7 @@ func (storageWatcher StorageWatcher) processRow(row utils.StorageDiffRow) {
 		return
 	}
 	executeErr := storageTransformer.Execute(row)
-	if executeErr != nil && executeErr != utils.ErrRowExists {
+	if executeErr != nil {
 		logrus.Warn(fmt.Sprintf("error executing storage transformer: %s", executeErr))
 		queueErr := storageWatcher.Queue.Add(row)
 		if queueErr != nil {
@@ -100,7 +100,7 @@ func (storageWatcher StorageWatcher) processQueue() {
 			continue
 		}
 		executeErr := storageTransformer.Execute(row)
-		if executeErr == nil || executeErr == utils.ErrRowExists {
+		if executeErr == nil {
 			storageWatcher.deleteRow(row.Id)
 		}
 	}

libraries/shared/watcher/storage_watcher_test.go

@@ -109,18 +109,6 @@ var _ = Describe("Storage Watcher", func() {
 				close(done)
 			})
 
-			It("does not queue row if transformer execution fails because row already exists", func(done Done) {
-				mockTransformer.ExecuteErr = utils.ErrRowExists
-
-				go storageWatcher.Execute(rows, errs, time.Hour)
-
-				Expect(<-errs).To(BeNil())
-				Consistently(func() bool {
-					return mockQueue.AddCalled
-				}).Should(BeFalse())
-				close(done)
-			})
-
 			It("queues row for later processing if transformer execution fails", func(done Done) {
 				mockTransformer.ExecuteErr = fakes.FakeError
 
@@ -199,17 +187,6 @@ var _ = Describe("Storage Watcher", func() {
 				close(done)
 			})
 
-			It("deletes row from queue if transformer execution errors because row already exists", func(done Done) {
-				mockTransformer.ExecuteErr = utils.ErrRowExists
-
-				go storageWatcher.Execute(rows, errs, time.Nanosecond)
-
-				Eventually(func() int {
-					return mockQueue.DeletePassedId
-				}).Should(Equal(row.Id))
-				close(done)
-			})
-
 			It("logs error if deleting persisted row fails", func(done Done) {
 				mockQueue.DeleteErr = fakes.FakeError
 				tempFile, fileErr := ioutil.TempFile("", "log")