diff --git a/config.go b/config.go
index 1347567d7..8a9183558 100644
--- a/config.go
+++ b/config.go
@@ -26,6 +26,10 @@ const AzureAPIKeyHeader = "api-key"
 
 const defaultAssistantVersion = "v2" // upgrade to v2 to support vector store
 
+type HTTPDoer interface {
+	Do(req *http.Request) (*http.Response, error)
+}
+
 // ClientConfig is a configuration of a client.
 type ClientConfig struct {
 	authToken string
@@ -36,7 +40,7 @@ type ClientConfig struct {
 	APIVersion           string // required when APIType is APITypeAzure or APITypeAzureAD
 	AssistantVersion     string
 	AzureModelMapperFunc func(model string) string // replace model to azure deployment name func
-	HTTPClient           *http.Client
+	HTTPClient           HTTPDoer
 
 	EmptyMessagesLimit uint
 }