assert: mock: I don't know what to return because the method call was unexpected Error while writing unit test in Go

Question

I am using testify in Go to write unit tests for my service methods and all the methods are working fine excepted the update method because in the update method I call another method("GetByID") of the same service inside the Update method.

Implementation of Update method in my service:

func (ts *teamService) Update(team *team.Team) AppError {
    t, err := ts.TeamRepo.GetByID(team.ID)
    if err != nil {
        return err
    }
    if t.TeamOwnerID != team.TeamOwnerID {
        return NewForbiddenError(forbiddenErr)
    }

    return ts.TeamRepo.Update(team)
}

MockRepo method for update:

func (t *teamRepoMock) Update(team *team.Team) AppError {
    args := t.Called(team)
    if args.Error(0) != nil {
        return NewNotFoundError(args.Error(0))
    }

    return nil
}

Implementation of the test:

func TestUpdate(t *testing.T) {
    _, teamIdGen, playerIdGen := setupConfig()

    t.Run("Update a team", func(t *testing.T) {
        teamRepo, _, ts := setupTeamService(teamIdGen, playerIdGen)

        teamRepo.On("Update", testTeam1).Return(nil)
        result := ts.Update(testTeam1)

        assert.Nil(t, result)
    })

    t.Run("Update a team fails", func(t *testing.T) {
        teamRepo, _, ts := setupTeamService(teamIdGen, playerIdGen)

        expected := oopsErr
        teamRepo.On("Update", testTeam1).Return(expected)
        result := ts.Update(testTeam1)

        assert.EqualValues(t, expected.Error(), result.Error())
    })
}

Now when I run the test I get the following error:

--- FAIL: TestUpdate (0.01s)
    --- FAIL: TestUpdate/Update_a_team (0.01s)
panic: 
assert: mock: I don't know what to return because the method call was unexpected.
    Either do Mock.On("GetByID").Return(...) first, or remove the GetByID() call.
    This method was unexpected:
        GetByID(string)
        0: ""
    at: [/home/waleem/Desktop/project/eazykhel_server/services/teamservice/team_service_init_test.go:18 /home/waleem/Desktop/project/eazykhel_server/services/teamservice/team_service.go:146 /home/waleem/Desktop/project/eazykhel_server/services/teamservice/team_service_test.go:277] [recovered]
    panic:

I tried calling mock.On("GetByID") before and after I call .On("Update") in my test function implementation and it didn't work and also I modified the mockRepo Update function but it didn't work.

Answer 1

Let me try to help you in figuring out the problem. I reproduced the repo with some simplification just to post the relevant code. If I'm not wrong in your solution there is a service ( TeamService ) that invokes some methods provided by an underlying package ( TeamRepo ). You wanna test the method Update method of the TeamService struct. After this recap, let me present the code first and I'll try to explain each file:

repo/repo.go

package repo

type Team struct {
    ID          int
    TeamOwnerID int
    Name        string
}

type TeamRepo struct{}

func (t *TeamRepo) GetByID(id int) (Team, error) {
    return Team{ID: id, TeamOwnerID: id, Name: "MyTeam"}, nil
}

func (t *TeamRepo) Update(team Team) error {
    return nil
}

Within this file, we can find the methods that we've to mock out. The methods are: GetByID and Update . Obviously, this is not your actual code but it doesn't matter for now.

services/service.go

package services

import (
    "errors"

    "testifymock/repo"
)

type TeamService struct {
    TR TeamRepoInterface
}

func NewTeamService(repo TeamRepoInterface) *TeamService {
    return &TeamService{
        TR: repo,
    }
}

type TeamRepoInterface interface {
    GetByID(id int) (repo.Team, error)
    Update(team repo.Team) error
}

func (ts *TeamService) Update(team *repo.Team) error {
    t, err := ts.TR.GetByID(team.ID)
    if err != nil {
        return err
    }

    if t.TeamOwnerID != team.TeamOwnerID {
        return errors.New("forbidden")
    }

    return ts.TR.Update(*team)
}

Here, we can see the service that will be our System Under Test ( sut ) in our test code. Through Dependency Injection, we'll take advantage of the capabilities provided by the repo package that is injected via the interface TeamRepoInterface .

services/service_test.go

package services

import (
    "errors"
    "testing"

    "testifymock/repo"

    "github.com/stretchr/testify/assert"
    "github.com/stretchr/testify/mock"
)

// 1. declare the mock struct
type teamRepoMock struct {
    mock.Mock
}

// 2. implement the interface
func (m *teamRepoMock) GetByID(id int) (repo.Team, error) {
    args := m.Called(id)

    return args.Get(0).(repo.Team), args.Error(1)
}

func (m *teamRepoMock) Update(team repo.Team) error {
    args := m.Called(team)

    return args.Error(0)
}

func TestUpdate(t *testing.T) {
    t.Run("GoodUpdate", func(t *testing.T) {
        // 3. instantiate/setup mock
        repoMock := new(teamRepoMock)
        repoMock.On("GetByID", 1).Return(repo.Team{ID: 1, TeamOwnerID: 1, Name: "test"}, nil).Times(1)
        repoMock.On("Update", repo.Team{ID: 1, TeamOwnerID: 1, Name: "test"}).Return(nil).Times(1)

        sut := NewTeamService(repoMock)
        err := sut.Update(&repo.Team{ID: 1, TeamOwnerID: 1, Name: "test"})

        // 4. check that all expectations were met on the mock
        assert.Nil(t, err)
        assert.True(t, repoMock.AssertExpectations(t))
    })

    t.Run("BadUpdate", func(t *testing.T) {
        // 3. instantiate/setup mock
        repoMock := new(teamRepoMock)
        repoMock.On("GetByID", 1).Return(repo.Team{ID: 1, TeamOwnerID: 1, Name: "test"}, nil).Times(1)
        repoMock.On("Update", repo.Team{ID: 1, TeamOwnerID: 1, Name: "test"}).Return(errors.New("some error while updating")).Times(1)

        sut := NewTeamService(repoMock)
        err := sut.Update(&repo.Team{ID: 1, TeamOwnerID: 1, Name: "test"})

        // 4. check that all expectations were met on the mock
        assert.Equal(t, "some error while updating", err.Error())
        assert.True(t, repoMock.AssertExpectations(t))
    })
}

Within the code, you can find some comments to better detail what's going on. As you've guessed the issue was this missing call in your code:

repoMock.On("GetByID", 1).Return(repo.Team{ID: 1, TeamOwnerID: 1, Name: "test"}, nil).Times(1)

If you run my solution, it should work also for you.
Let me know if this solves your issue or if there are any other problems!