Replace App.HTTPClient calls after merge (#9387)

* Replace App.HTTPClient calls after merge

* Add missing import

app/post_test.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"net/http"
 	"net/http/httptest"
+	"strings"
 	"sync/atomic"
 	"testing"
 	"time"