Mock inner function in golang - go

Question

I want to mock function using interface and I was able to mock the first function callsomething
With great help from icza , Now it’s a bit more tricky . I want to test function vl1
With mock for function function1 , how it can be done.
https://play.golang.org/p/w367IOjADFV
package main
import (
"fmt"
"time"
"testing"
)
type vInterface interface {
function1() bool
}
type mStruct struct {
info string
time time.Time
}
func (s *mStruct) function1() bool {
return true
}
func callSomething(si vInterface) bool {
return si.function1()
}
func (s *mStruct) vl1() bool {
return callSomething(s)
}
var currentVt1 mStruct
func main() {
vl1 := currentVt1.vl1()
fmt.Println(vl1)
}
//——————————————————TESTS——————————————————
// This test is working as expected (as suggested by icza) for the function "callSomething"
// here we use mock interface and mock function which helps to mock function1
type mockedVInterface struct {
value bool
}
func (m mockedVInterface) fn1() bool {
return m.value
}
func Test_callSomething(t *testing.T) {
type args struct {
si vInterface
}
tests := []struct {
name string
args args
want bool
}{
{
name: "first value",
args: args{
si: mockedVInterface{value: false},
},
want: false,
},
{
name: "second value",
args: args{
si: mockedVInterface{value: true},
},
want: true,
},
}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
if got := callSomething(tt.args.si); got != tt.want {
t.Errorf("callSomething() = %v, want %v", got, tt.want)
}
})
}
}
//----Here is the test which a bit tricky
//I want to call to "s.vl1()" and test it with mock for "function1"
func Test_mStruct_vl1(t *testing.T) {
type fields struct {
info string
time time.Time
}
tests := []struct {
name string
fields fields
want bool
}{
{
name: "test 2",
fields: struct {
info string
time time.Time
}{info: "myinfo", time: time.Now() },
},
}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
s := &mStruct{
info: tt.fields.info,
time: tt.fields.time,
}
//here the test is starting
if got := s.vl1(); got != tt.want {
t.Errorf("mStruct.vl1() = %v, want %v", got, tt.want)
}
})
}
}

Answer 1

If you want to mock a function in Go you'll have to declare a variable that will hold the function value, have all callers of the function use the variable instead and then during tests you can switch up the function value for a mock implementation.
func callSomethingFunc(si vInterface) bool {
return si.function1()
}
var callSomething = callSomethingFunc
func (s *mStruct) vl1() bool {
return callSomething(s)
}
// ...
func Test_mStruct_vl1(t *testing.T) {
callSomething = func(si vInterface) bool { // set mock
// do mock stuff
}
defer func(){
callSomething = callSomethingFunc // set back original func at end of test
}()
// ...