Return an error instead of panic

cache.go

@@ -400,26 +400,25 @@ func (cache *Cache) Stats() Stats {
 }
 
 // Resize the cache to hold at most n entries. If n is smaller than the current
-// size, entries are evicted to fit the new size.
-func (cache *Cache) Resize(n int) {
+// size, entries are evicted to fit the new size. It errors if n <= 0.
+func (cache *Cache) Resize(n int) error {
 	if n <= 0 {
-		panic("Must supply a positive capacity to Resize")
+		return errors.New("must supply a positive capacity to Resize")
 	}
 
 	cache.mutex.Lock()
 	defer cache.mutex.Unlock()
 	c := cache.capacity
 	cache.capacity = n
 
-	if n >= c {
-		return
-	}
-	for i := 0; i <  c - n; i++ {
+	for i := 0; i < c-n; i++ {
 		successful := cache.evictOldest()
 		if !successful {
 			break
 		}
 	}
+
+	return nil
 }
 
 func (cache *Cache) deleteExpired() {