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How To Generate Mocks with Mockery

Mockery provides the ability to easily generate mocks for golang interfaces. It removes the boilerplate coding required to use mocks.

In Golang, mocks can only be created on interfaces - not structs. So, it is important that for whichever mock you are trying to generate, it should correspond to the appropriate interface.

Auto-generating mocks with go generate​

The make mocks_generate command will regenerate mocks for all interfaces tagged with the appropriate go generate command. To add an interface to the list of auto-generated mocks, just add a go:generate comment like below and update the name with your interface name.

// AccessCodeClaimer is the service object interface for ValidateAccessCode
//go:generate mockery -name AccessCodeClaimer
type AccessCodeClaimer interface {
    ClaimAccessCode(code string, serviceMemberID uuid.UUID) (*models.AccessCode, *validate.Errors, error)
}

Using Mocks​

When you use the mock type, you need to know two things:

  1. What you expect to receive as input.
  2. What you expect to receive as output.
Pointers in Mocks

These should be defined as exactly as possible to preserve the integrity of your test. If you have to include pointer input, you must always use copies of the pointer and never, ever use that specific pointer again. Otherwise, you could unknowingly change the input you expect and your test would be compromised.

If you are unsure about the inputs/returns for a mock, you should not use a mock.

Example test mock
reweigh := testdatagen.MakeDefaultReweigh(suite.DB())
reweighCopy := *reweigh // make sure the copy is a value, not a pointer

updater := mocks.NewReweighUpdater(suite.T())

updater.On("UpdateReweigh",
    mock.AnythingOfType("appcontext.AppContext"), // you can include as many input parameters
    mock.AnythingOfType("*models.Reweigh")        // as you need
).Return(reweighCopy, nil)

Note that this calls the generated mock function, not the original.

More mocking

Use MockedInterface.On() to mock a method.

Mocks also have a AssertExpectations method to validate expectations, such as parameter type and number of times the method was called. When you use mocks.New<MockedThing>, it automatically sets it up to call AssertExpectations at the end.

See testify's docs for more information.