Update OpenIddictMongoDbTestModule.cs

modules/openiddict/test/Volo.Abp.OpenIddict.MongoDB.Tests/Volo/Abp/OpenIddict/MongoDB/OpenIddictMongoDbTestModule.cs

@@ -20,9 +20,10 @@ public class OpenIddictMongoDbTestModule : AbpModule
 
     public override void ConfigureServices(ServiceConfigurationContext context)
     {
+        _connectionString = MongoDbFixture.GetRandomConnectionString();
         Configure<AbpDbConnectionOptions>(options =>
         {
-            options.ConnectionStrings.Default = MongoDbFixture.GetRandomConnectionString();
+            options.ConnectionStrings.Default = _connectionString;
         });
     }