fix and document test case

Author: atantawi

pkg/quotaplugins/quota-forest/quota-manager/README.md

@@ -189,6 +189,7 @@ A summary of the API interface to the Quota Manager follows.
   - refresh (effect) updates from caches
     - `UpdateForest(forestName)`
 - Undo consumer allocation: Two calls are provided to try to allocate a consumer, and if unaccepted, to undo the effect of the allocation trial. If the trial is accepted, no further action is needed. Otherwise, the undo has to be called right after the try allocation, without making any calls to change the trees or allocate/deallocate consumers. These operations are intended only during Normal mode.
+(Note: This design pattern puts the burden on the caller of the quota manager to make sure that TryAllocate() and UndoAllocate() are run in an atomic fashion. So, a lock is needed for that purpose. An example is provided in the TestQuotaManagerParallelTryUndoAllocation() in [quotamanagerundo_test.go](quota/quotamanagerundo_test.go))
   - `TryAllocate(treeName, consumerID)`
   - `UndoAllocate(treeName, consumerID)`
   - `TryAllocateForest(forestName, consumerID)`

pkg/quotaplugins/quota-forest/quota-manager/quota/quotamanagerundo_test.go

@@ -328,7 +328,7 @@ func TestTreeAllocateTryAndUndo(t *testing.T) {
 func TestForestAllocateTryAndUndo(t *testing.T) {
 	forestName := "testForest"
 	forestTreesSpecs := []string{testTreeSpec, serviceTreeSpec}
-	var err error
+
 	// define tests
 	var tests = []struct {
 		name         string
@@ -410,6 +410,7 @@ func TestForestAllocateTryAndUndo(t *testing.T) {
 		tt := tt
 		t.Run(tt.name, func(t *testing.T) {
 			t.Parallel()
+			var err error
 			// After keeps the state of the quota manager after applying a test case
 			qmAfter := quota.NewManager()
 			initializeForestQuotaManager(t, qmAfter, forestName, forestTreesSpecs, testForestConsumersSpecMap,