htlcswitch+peer: add trivial implementations for flush api to mocks

Author: ProofOfKeags

htlcswitch/mock.go

@@ -906,10 +906,11 @@ func (f *mockChannelLink) UpdateShortChanID() (lnwire.ShortChannelID, error) {
 	return f.shortChanID, nil
 }
 func (f *mockChannelLink) Flush(onFlushed func()) error {
-	return errors.New("mockChannelLink does not support flush api")
+	onFlushed()
+	return nil
 }
 func (f *mockChannelLink) CancelFlush() error {
-	return errors.New("mockChannelLink does not support flush api")
+	return errors.New("no flush in progress to cancel")
 }
 func (f *mockChannelLink) IsFlushing() bool {
 	return false

peer/test_utils.go

@@ -500,12 +500,13 @@ type mockMessageConn struct {
 	curReadMessage []byte
 }
 
-func (m *mockUpdateHandler) Flush(func()) error {
-	return errors.New("mockUpdateHandler does not support flush api")
+func (m *mockUpdateHandler) Flush(onFlushed func()) error {
+	onFlushed()
+	return nil
 }
 
 func (m *mockUpdateHandler) CancelFlush() error {
-	return errors.New("mockUpdateHandler does not support flush api")
+	return errors.New("no flush in progress to cancel")
 }
 
 func (m *mockUpdateHandler) IsFlushing() bool {