[Chore] Add tests for cache builder

builder.go

@@ -21,7 +21,8 @@ type options[K comparable, V any] struct {
 }
 
 func (o *options[K, V]) validate() error {
-	if o.shardCount == illegalShardCount {
+	// shard count should be power of two.
+	if o.shardCount <= 0 || (o.shardCount&(o.shardCount-1)) != 0 {
 		return ErrIllegalShardCount
 	}
 

builder_test.go

@@ -0,0 +1,47 @@
+package otter
+
+import (
+	"errors"
+	"reflect"
+	"testing"
+)
+
+func TestBuilder_NewFailed(t *testing.T) {
+	_, err := NewBuilder[int, int](-63)
+	if err == nil || !errors.Is(err, ErrIllegalCapacity) {
+		t.Fatalf("should fail with an error %v, but got %v", ErrIllegalCapacity, err)
+	}
+}
+
+func TestBuilder_BuildFailed(t *testing.T) {
+	b, err := NewBuilder[int, int](10)
+	if err != nil {
+		t.Fatalf("builder creates with error %v", err)
+	}
+
+	_, err = b.ShardCount(129).Build()
+	if err == nil || !errors.Is(err, ErrIllegalShardCount) {
+		t.Fatalf("should fail with an error %v, but got %v", ErrIllegalShardCount, err)
+	}
+}
+
+func TestBuilder_BuildSuccess(t *testing.T) {
+	b, err := NewBuilder[int, int](10)
+	if err != nil {
+		t.Fatalf("builder creates with error %v", err)
+	}
+
+	c, err := b.
+		ShardCount(256).
+		StatsEnabled(true).
+		Cost(func(key int, value int) uint32 {
+			return 2
+		}).Build()
+	if err != nil {
+		t.Fatalf("builded cache with error: %v", err)
+	}
+
+	if !reflect.DeepEqual(reflect.TypeOf(&Cache[int, int]{}), reflect.TypeOf(c)) {
+		t.Fatalf("builder returned a different type of cache: %v", err)
+	}
+}