Mongodb Go mongo驱动程序测试，FindOne未根据给定的筛选器返回正确结果

我有一个函数，它应该根据MongoDB a org的过滤器返回，实际上它工作得很好.

func (m *MongoSysService) GetOrg(org string) (types.Org, error) {
    var data types.Org
    if err := m.org.FindOne(context.Background(), bson.D{{Key: "_id", Value: org}}).Decode(&data); err != nil {
        return types.Org{}, err
    }
    return data, nil
}

但后来我试着用mtest来模拟它，结果总是返回第一个结果org1，无论我怎么try ，都找不出问题所在.

func TestMongoSysService_GetOrg(t *testing.T) {
    mt := mtest.New(t, mtest.NewOptions().ClientType(mtest.Mock))
    defer mt.Close()

    mt.Run("success", func(mt *mtest.T) {
        mongoDB.org = mt.Coll

        first := mtest.CreateCursorResponse(1, "foo.bar", mtest.FirstBatch, bson.D{
            {Key: "_id", Value: "org1"},
            {Key: "name", Value: "org1"},
            {Key: "api", Value: "key1"},
        })

        second := mtest.CreateCursorResponse(2, "foo.bar", mtest.NextBatch, bson.D{
            {Key: "_id", Value: "org2"},
            {Key: "name", Value: "org2"},
            {Key: "api", Value: "key2"},
        })

        third := mtest.CreateCursorResponse(3, "foo.bar", mtest.NextBatch, bson.D{
            {Key: "_id", Value: "org3"},
            {Key: "name", Value: "org3"},
            {Key: "api", Value: "key3"},
        })

        killCursors := mtest.CreateCursorResponse(0, "foo.bar", mtest.NextBatch)

        mt.AddMockResponses(first, second, third, killCursors)

        result, err := mongoDB.GetOrg("org2")
        if err != nil {
            t.Fatal(err)
        }
        if result.Name != "org2" || result.GoogleAPIKey != "key2" {
            t.Errorf("Expected %s and %s, got %s and %s", "org2", "key2", result.Name, result.GoogleAPIKey)
        }
    })
}

使用相同的测试用例，我试图在cursor上使用Find来查找所有记录，它在模拟中起作用，当模拟它在Find上时，我得到所有3个记录.

这里的问题可能是什么？

我用的是go.mongodb.org/mongo-driver v1.5.4和go1.9