gomock

README

gomock example

Using gomock on an interface and using the go tool gotests for unit testing.

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WHAT IS GOMOCK

GoMock is a mock framework for Go. Its useful for mocking an interface It enjoys a somewhat official status as part of the github.com/golang organization. mockgen is the code generation tool.

Install,

go get -u -v github.com/golang/mock/gomock
go install github.com/golang/mock/mockgen

Verify you have it,

$GOPATH/bin/mockgen

HOW TO USE GOMOCK

Four basic steps:

• Use mockgen to generate a mock for the interface you wish to mock
• In your test, create an instance of gomock.Controller and pass it to your mock object’s constructor to obtain a mock object
• Call EXPECT() on your mocks to set up their expectations and return values
• Call Finish() on the mock controller to assert the mock’s expectations

More on this in a bit. First lets look at the packages.

CREATURES PACKAGE

Lets describe a werewolf and a vampire in our creatures package /creatures/creatures.go,

type Werewolf struct {
    TimeofDay string
}
type Vampire struct {
    Age int
}

Where werewolf has the following methods,

• Kind() - during day is a human, otherwise werewolf.
• Fly() - no
• Sound() - during days says "hell0" otherwise "howls".

And vampire has the following methods,

• Kind() - older than 100, he's a vampire.
• Fly() - yes
• Sound() - "I want to drink your blood"

LABORATORY PACKAGE

I created another package laboratory where I keep my creatures.

type Creatures interface {
    Kind() string
    Fly() bool
    Sound() string
}

Where I have two functions Greet and FlyAway using the interface.

RUN

go run helloween.go

GENERATE TEST FILE USING GOTESTS

The following command will generate a test file with the hooks in place to perform unit testing,

cd laboratory
gotests -w -all .
cd creatures
gotests -w -all .

RUN YOUR TEST & COVERAGE (0% COVERED)

Now if you run go test,

cd ..
go test -v -cover laboratory/*
go test -v -cover creatures/*

Optional commands,

go test -coverprofile coverage.out
go tool cover -html=coverage.out -o coverage.html

You should get 0% covered,

PASS
coverage: 0.0% of statements

ADD TESTS TO CREATURES PACKAGE (100% COVERED)

There are 6 methods in the creatures package.

As an example lets add tests to the function TestWerewolf_Kind(t *testing.T),

        // TODO: Add test cases.
        {
            "Test1",
            fields{
                TimeofDay: "day",
            },
            "human",
        },
        {
            "Test2",
            fields{
                TimeofDay: "night",
            },
            "werewolf",
        },

Do this for all six methods in the creatures package. Now when you run your test,

cd creatures
go test -v -cover .
go test -coverprofile coverage.out
go tool cover -html=coverage.out -o coverage.html

Your coverage shall now be,

PASS
coverage: 100% of statements

ADD TESTS TO LABORATORY PACKAGE (100% COVERED)

We have two functions to test; Greet() and FlyAway() that each use an interface. So lets mock that interface.

Using mockgen, we create a file mockcreature.go,

cd laboratory
mockgen -source=laboratory.go -package=laboratory -destination=mockcreature.go

To use add the following lines to the top of your test function func TestGreet(t *testing.T) {

func TestGreet(t *testing.T) {
    var ctrl = gomock.NewController(t)
    defer ctrl.Finish()
    var mockcreature = NewMockCreatures(ctrl)
    mockcreature.EXPECT().Sound().Times(1).Return("poo")

Where you test is,

        // TODO: Add test cases.
        {
            "Test1",
            args{
                c: mockcreature,
            },
            "poo",
        },

Do the same to the other function. Now run your tests,

cd laboratory
go test -v -cover .
go test -coverprofile coverage.out
go tool cover -html=coverage.out -o coverage.html