moved options into their own file and more tests

options.go

@@ -1,23 +1,29 @@
 package gubgub
 
+import (
+	"sync"
+)
+
 // TopicOptions holds common options for topics.
 type TopicOptions struct {
-	// onClose is called after the Topic is closed and all messages have been delivered.
+	// onClose is called after the Topic is closed and all messages have been delivered. Even
+	// though you might call Close multiple times, topics are effectively closed only once thus
+	// this should be called only once.
 	onClose func()
 
 	// onSubscribe is called after a new subscriber is regitered.
-	onSubscribe func(count int)
+	onSubscribe func()
 }
 
 type TopicOption func(*TopicOptions)
 
 func WithOnClose(fn func()) TopicOption {
 	return func(opts *TopicOptions) {
-		opts.onClose = fn
+		opts.onClose = sync.OnceFunc(fn)
 	}
 }
 
-func WithOnSubscribe(fn func(count int)) TopicOption {
+func WithOnSubscribe(fn func()) TopicOption {
 	return func(opts *TopicOptions) {
 		opts.onSubscribe = fn
 	}