How to mock mongo with this interface?

[snavarro89]

If I have the following code

mycollection := mongo.Database("mydb").Collection("mycollection")
var record interface{}
err = mycollection.FindOne(context.TODO(), bson.M{}).Decode(&record)

How can I mock FindOne and specify what data should be decoded into "record" ?

If I were to do that for another 50 db calls, is it possible to establish what a specific call should be returning when the test is run?

[SVilgelm]

oh, thank you. It is very good question. But before answer let me add the mocks to this repo, I think it will be much easier if the repo will contain mocks as well

[SVilgelm]

OK. Here is an example of how to mock the mongo objects

Let's say we have a function that returns all admin users:

package simple

import (
	"context"

	"go.mongodb.org/mongo-driver/bson/primitive"

	"github.com/sv-tools/mongoifc"
)

const (
	UsersCollection = "users"
)

type User struct {
	ID primitive.ObjectID `json:"id,omitempty" bson:"_id,omitempty"`
	Name string `json:"name,omitempty" bson:"name,omitempty"`
	Email string `json:"email,omitempty" bson:"email,omitempty"`
	Active bool `json:"active,omitempty" bson:"active,omitempty"`
	IsAdmin bool `json:"is_admin,omitempty" bson:"is_admin,omitempty"`
}

func GetAdmins(ctx context.Context, db mongoifc.Database) ([]*User, error) {
	var users []*User
	cur, err := db.Collection(UsersCollection).Find(ctx, User{
		Active: true,
		IsAdmin: true,
	})
	if err != nil {
		return nil, err
	}
	if err := cur.Decode(&users); err != nil {
		return nil, err
	}
	return users, err
}

and here is the test, actually two tests. First test uses mockery and second uses gomock:

package simple

import (
	"context"
	"testing"

	"github.com/golang/mock/gomock"
	"github.com/stretchr/testify/mock"
	"github.com/stretchr/testify/require"

	gomockMocks "github.com/sv-tools/mongoifc/mocks/gomock"
	mockeryMocks "github.com/sv-tools/mongoifc/mocks/mockery"
)

func TestGetAdmins(t *testing.T) {
	expectedUsers := []*User{
		{Name: "foo", Active: true, IsAdmin: true},
		{Name: "bar", Active: true, IsAdmin: true},
	}
	ctx := context.Background()

	t.Run("mockery", func(t *testing.T) {
		cur := &mockeryMocks.Cursor{}
		cur.On("Decode", mock.Anything).Run(func(args mock.Arguments) {
			users := args[0].(*[]*User)
			*users = append(*users, expectedUsers...)
		}).Return(nil)

		col := &mockeryMocks.Collection{}
		col.On("Find", ctx, mock.AnythingOfType("User")).Return(cur, nil)

		db := &mockeryMocks.Database{}
		db.On("Collection", UsersCollection).Return(col)

		users, err := GetAdmins(ctx, db)
		require.NoError(t, err)
		require.Equal(t, expectedUsers, users)
	})

	t.Run("gomock", func(t *testing.T) {
		ctrl := gomock.NewController(t)
		defer ctrl.Finish()

		cur := gomockMocks.NewMockCursor(ctrl)
		cur.EXPECT().Decode(gomock.Any()).Do(func(arg interface{}) {
			users := arg.(*[]*User)
			*users = append(*users, expectedUsers...)
		}).Return(nil)

		col := gomockMocks.NewMockCollection(ctrl)
		col.EXPECT().Find(ctx, gomock.Any()).Return(cur, nil)

		db := gomockMocks.NewMockDatabase(ctrl)
		db.EXPECT().Collection(UsersCollection).Return(col)

		users, err := GetAdmins(ctx, db)
		require.NoError(t, err)
		require.Equal(t, expectedUsers, users)
	})
}

[SVilgelm]

This example can be found here: https://github.com/sv-tools/mongoifc/tree/main/examples/simple
Als the README is updated