mockery ¶

Mockery is a project that creates mock implementations of Golang interfaces. The mocks generated in this project are based off of the github.com/stretchr/testify suite of testing packages.

Why mockery? ¶

When you have an interface like this:

db.go

 type DB interface {
     Get(val string) string
 }

and a function that takes this interface:

db_getter.go

 func getFromDB(db DB) string {
     return db.Get("ice cream")
 }

You can test getFromDB by either instantiating a testing database, or you can simply create a mock implementation of DB using mockery. Mockery can automatically generate a mock implementation that allows us to define assertions on how the mock was used, what to return, and other useful tidbits. We can add a //go:generate directive above our interface:

db.go

 //go:generate mockery --name DB
 type DB interface {
     Get(val string) string
 }

.mockery.yaml

 inpackage: True # (1)!
 with-expecter: True # (2)!
 testonly: True # (3)!

Generate our mocks next to the original interface
Create expecter methods
Append _test.go to the filename so the mock object is not packaged

Bash

 $ go generate  
 05 Mar 23 21:49 CST INF Starting mockery dry-run=false version=v2.20.0
 05 Mar 23 21:49 CST INF Using config: .mockery.yaml dry-run=false version=v2.20.0
 05 Mar 23 21:49 CST INF Walking dry-run=false version=v2.20.0
 05 Mar 23 21:49 CST INF Generating mock dry-run=false interface=DB qualified-name=github.com/vektra/mockery/v2/pkg/fixtures/example_project version=v2.20.0

We can then use the mock object in a test:

db_getter_test.go

 import (
     "testing"
 
     "github.com/stretchr/testify/assert"
 )
 
 func Test_getFromDB(t *testing.T) {
     mockDB := NewMockDB(t)
     mockDB.EXPECT().Get("ice cream").Return("chocolate").Once()
     flavor := getFromDB(mockDB)
     assert.Equal(t, "chocolate", flavor)
 }

Why use mockery over gomock? ¶

mockery provides a much more user-friendly API and is less confusing to use
mockery utilizes testify which is a robust and highly feature-rich testing framework
mockery has rich configuration options that allow fine-grained control over how your mocks are generated
mockery's CLI is more robust, user-friendly, and provides many more options
mockery supports generics (this may no longer be an advantage if/when gomock supports generics)

Who uses mockery? ¶

Grafana
Google Skia
Google Skyzkaller
Hashicorp
Uber Cadence
Jaegertracing
Splunk kafka-mq-go
eksctl
Task

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