C# 使用Owin TestServer时返回的异常未完成

我有一个web api，我想测试它。当我使用browser调用它时，它会返回一个json，如：

{
    message: "An error has occurred.",
    exceptionMessage: "Self referencing loop detected with type ......",
    exceptionType: "Newtonsoft.Json.JsonSerializationException",
    stackTrace: " at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.CheckForCircularReference(JsonWriter writer, Object value, JsonProperty property, JsonContract contract, JsonContainerContract containerContract, JsonProperty containerProperty) 
                    at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IEnumerable values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty) 
                    at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue(JsonWriter writer, Object value, JsonContract valueContract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerProperty) 
                    "
}

但当我在单元测试中使用Owin

TestServer

调用它时，它只返回一个简单的json，没有所有细节：

{
    message: "An error has occurred."
}

在我的单元测试中，我这样调用api：

var response = OwinServer.HttpClient.GetAsync("api/Products/GetAll").Result;
if (response.StatusCode != HttpStatusCode.OK)
{
    var errorStr = response.Content.ReadAsStringAsync().Result;
    Assert.Fail(errorStr)   // this errorStr is not complete enough!
}

如果出现完全错误，特别是堆栈跟踪，我该怎么办