Create a mock function

Question

Hi I would like to test or Mock a certain function and return a Mock response for this. To demonstrate below is my code

Sample.go

package main

import (
    "fmt"

    log "github.com/sirupsen/logrus"
)

var connectDB = Connect

func Sample() {
    config := NewConfig()
    response := connectDB(config)
    fmt.Println(response)
    log.Info(response)
}

func Connect(config *Config) string {
    return "Inside the connect"
}

And my test is like this

Sample_test.go

package main

import (
    "testing"
)

func TestSample(t *testing.T) {

    oldConnect := connectDB
    connectDB := func(config *Config) string {
        return "Mock response"
    }
    defer func() { connectDB = oldConnect }()

    Sample()
}

So when running go test I was expecting to receive and output of Mock response but I'm still getting Inside the connect. Is there something I'm missing here?

Answer 1

@jrefior is correct, but I'd suggest to use interface for mocking. Of course, it's up to you, bet for me it is more clear, but more complicated code :)

// lack some fields :)
type Config struct {
}

// Use interface to call Connect method
type IConnection interface {
    Connect(config *Config) string
}

// Real connection to DB
type Connection struct {
}

func (c Connection) Connect(config *Config) string {
    return "Inside the connect"
}

// Mock connection
type MockConnection struct {
}

func (c MockConnection) Connect(config *Config) string {
    return "Mock connection"
}

// Accepts interface to connect real or mock DB
func Sample(con IConnection) {
    log.Println(con.Connect(nil))
}


func main() {
    realConnection := Connection{}
    Sample(realConnection)

    mockConnection := MockConnection{}
    Sample(mockConnection)
}

Answer 2

The use of a colon here creates a new function-scoped variable with the same name:

connectDB := func(config *Config) string {
    return "Mock response"
}

Remove the colon to assign to the package variable.