使用mongo-go-driver模拟Aggregate遇command failed错误求解决

我尝试模拟MongoDB的Aggregate函数，但它持续返回通用错误command failed。

待测试函数 #

func (b *BlogsRepo) CountTagsInBlogs(ctx context.Context) (map[string]int, error) {
    clog := log.GetLoggerFromContext(ctx)

    // 指定分组统计标签的管道
    pipeline := []bson.M{
        {
            "$unwind": "$tags",
        },
        {
            "$group": bson.M{
                "_id":   "$tags",
                "count": bson.M{"$sum": 1},
            },
        },
    }

    // 根据管道聚合数据
    cursor, err := b.collection.Aggregate(ctx, pipeline)
    if err != nil {
        clog.ErrorCtx(err, log.Ctx{
            "msg": "Error aggregating data",
            "err": err,
        })

        return nil, err
    }
    defer cursor.Close(ctx)

    // 创建存储标签计数的map
    tagCounts := make(map[string]int)

    // 遍历结果并填充map
    for cursor.Next(ctx) {
        var result struct {
            Tag   string `bson:"_id"`
            Count int    `bson:"count"`
        }
        if err := cursor.Decode(&result); err != nil {
            clog.ErrorCtx(err, log.Ctx{
                "msg": "Error decoding result"},
            )

            return nil, err
        }
        tagCounts[result.Tag] = result.Count
    }

    return tagCounts, nil
}

测试代码 #

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

    testCases := []struct {
        name           string
        mockedResponse []bson.D
        expected       map[string]int
        err            error
    }{
        {
            name: "successful count tags response",
            mockedResponse: []bson.D{
                {{"_id", "java"}, {"count", 3}},
                {{"_id", "go"}, {"count", 7}},
                {{"_id", "kotlin"}, {"count", 3}},
            },
            expected: map[string]int{
                "java":   3,
                "go":     7,
                "kotlin": 3,
            },
            err: nil,
        },
    }

    for _, tc := range testCases {
        tc := tc
        mt.Run(tc.name, func(mt *mtest.T) {
            // 模拟聚合响应
            mt.AddMockResponses(tc.mockedResponse...)

            blogRepo := NewBlogRepository(mt.Client, mt.Coll)

            // 调用待测试方法
            tagCounts, err := blogRepo.CountTagsInBlogs(ctx)

            // 校验返回值与预期是否一致
            assert.Equal(t, tc.expected, tagCounts, "Tag counts do not match expected values")
            assert.NoError(t, err)

        })
    }
}

报错信息 #

Error:          Received unexpected error:
                command failed
Test:           TestBlogsRepo_CountTagsInBlogs

错误发生在以下代码段：

cursor, err := b.collection.Aggregate(ctx, pipeline)
if err != nil {
    clog.ErrorCtx(err, log.Ctx{
        "msg": "Error aggregating data",
        "err": err,
    })

    return nil, err
}
defer cursor.Close(ctx)

捕获该错误后会返回nil map，进而导致与预期结果不匹配。我认为自己的Mock配置没有问题，希望能得到解决建议。

内容的提问来源于stack exchange，提问作者Mike3355