Add NumOperations() method to Transaction.

Useful for checking if the transation is empty
before trying to execute it, for example.

fake_test.go

@@ -307,6 +307,10 @@ func TestFakeCheck(t *testing.T) {
 	fake := NewFake(IPv4Family, "kube-proxy")
 
 	tx := fake.NewTransaction()
+
+	if tx.NumOperations() != 0 {
+		t.Errorf("empty transaction should have 0 operations, got %d", tx.NumOperations())
+	}
 
 	tx.Add(&Table{})
 	tx.Add(&Chain{
@@ -335,6 +339,10 @@ func TestFakeCheck(t *testing.T) {
 		t.Errorf("unexpected transaction content:\n%s", diff)
 	}
 
+	if tx.NumOperations() != 4 {
+		t.Errorf("unexpected number of operations: expected 4, got %d", tx.NumOperations())
+	}
+
 	err := fake.Run(context.Background(), tx)
 	if err != nil {
 		t.Fatalf("unexpected error from Run: %v", err)

transaction.go

@@ -76,6 +76,11 @@ func (tx *Transaction) String() string {
 	return buf.String()
 }
 
+// NumOperations returns the number of operations queued in the transaction.
+func (tx *Transaction) NumOperations() int {
+	return len(tx.operations)
+}
+
 func (tx *Transaction) operation(verb verb, obj Object) {
 	if tx.err != nil {
 		return