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mongodb - Mocking official MongoDb driver

问题描述

I need to define these interfaces to mock official mongo driver

type MgCollection interface {   
    FindOne(ctx context.Context, filter interface{}, opts ...*options.FindOneOptions) *mongo.SingleResult
    // Other methods
}

type MgDatabase interface {
    Collection(name string, opts ...*options.CollectionOptions) MgCollection
    // Other methods
}

In mongo driver package there are two structs mongo.Collection and mongo.Database with these methods

func (coll *Collection) FindOne(ctx context.Context, filter interface{}, opts ...*options.FindOneOptions) *SingleResult {
    // Method code
}

func (db *Database) Collection(name string, opts ...*options.CollectionOptions) *Collection {
    // Method code
}

The struct *mongo.Collection implement MgCollection correctly, so this code compiles without error

var col mgdriver.MgCollection
col = &mongo.Collection{}
col.FindOne(ctx, nil, nil)

But The struct *mongo.Database not implement MgDatabase, so I when I write something like this:

var db mgdriver.MgDatabase
db = &mongo.Database{}
db.Collection("Test", nil)

Compiler show this error:

cannot use &mongo.Database literal (type *mongo.Database) as type mgdriver.MgDatabase in assignment: *mongo.Database does not implement mgdriver.MgDatabase (wrong type for Collection method) have Collection(string, ...*options.CollectionOptions) *mongo.Collection want Collection(string, ...*options.CollectionOptions) mgdriver.MgCollection

Both mongo.Collection and mongo.Database are in the official package and I cannot change any code in that package. so how can I change my interfaces to mock official mongo driver correctly?

标签： mongodbunit-testinggomocking

解决方案

通常，您不会。你应该做的是定义一个数据访问接口，

type CRUD interface {
  Create(yourModel) error
  Read(page, size, skip) []yourModel
  Update(yourModel) error
  Delete(yourModel) error
}

并实施。

然后模拟接口，例如使用testify/mock：

type MockedCRUD struct {
  mock.Mock
}

func(m *MockedCRUD)Create(y yourModel) error{
  returned m.Called(y).Error(0)
}
// And so on and so forth

由于MockedCRUD满足 CRUD 接口，你可以像使用你的MongoCRUD实现一样使用它，没有任何麻烦：

func TestYourApplicationLogicCallingCreate( t *testing.T){
    model := YourModel{Type: ”Baz”})

    mocked := new(MockedCRUD)
    mocked.On(”Create”,model).Return(ErrInvalidType)

    app := YourApplication{CRUD:mocked}

    err := app.yourApplicationLogicCallingCreate(model)

    assert.Error(t,err)
    assert.Equal(t,ErrInvalidType,err)

}

仍然是如何测试 CRUD 接口的实现的问题。我曾经使用最初由 Gustavo Niemeyer 开发并由 globalsign 接管的 mgo 驱动程序。这带来了一个漂亮的小包，叫做dbtest。它实际上是一个非常薄的 MongoDB 实例包装器，可以按需启动和停止一个实例，并能够在测试之间重置数据。要么只是导入dbtest，要么引用一句 Go Proverb

一点点复制比一点点依赖要好。

（但请记住给予信用，并保留版权说明。）

因此，使用上述方法，您可以非常快速地针对模拟进行单元测试，并为您的测试量身定制稳定且可预测的答案，并且仅在绝对必须的情况下针对 MongoDB 进行相对昂贵且速度较慢的测试。

额外的好处：更换您的实际持久性技术相对容易。

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