Storage: Fix Preconditions checks in tests (#510)

Author: schmidt-sebastian

firebase-storage/src/testUtil/java/com/google/firebase/storage/TestDownloadHelper.java

@@ -267,15 +267,17 @@ private static void verifyTaskCount(StorageReference reference, int expectedTask
     Preconditions.checkState(
         globalDownloadTasks.size() == expectedTasks,
         "Expected active download task to contain %s item(s), but contained %s item(s)",
-        globalDownloadTasks.size());
+        globalDownloadTasks.size(),
+        expectedTasks);
     List<FileDownloadTask> downloadTasksAtParent =
         StorageTaskManager.getInstance().getDownloadTasksUnder(reference.getParent());
     Preconditions.checkState(
         downloadTasksAtParent.size() == expectedTasks,
         "Expected active download task at location %s to contain %s item(s), "
             + "but contained %s item(s)",
         reference.getParent(),
-        downloadTasksAtParent.size());
+        downloadTasksAtParent.size(),
+        expectedTasks);
   }
 
   private static String fileTaskToString(FileDownloadTask.TaskSnapshot state) {