How to use function interface with diff implementation - go

Question

Im using interface which I want to mock one method in it function1 in test and I wasn't able to figure it out how is the best to do it that for prod code it will provide 1 value and for test provide some mock value , can someone please give example ? (edited)
this is the code:
https://play.golang.org/p/w367IOjADFV
package main
import (
"fmt"
"time"
)
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 {
s.time = time.Now()
s.info = "vl1->info"
return callSomething(s)
}
var currentVt1 mStruct
func main() {
vl1 := currentVt1.vl1()
fmt.Println(vl1)
}
The test is like this
func Test_callSomething(t *testing.T) {
type args struct {
si vInterface
}
tests := []struct {
name string
args args
want bool
}{
{
name: "my tests",
args: args{
},
want: false,
},
}
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)
}
})
}
}
But not sure how to mock it right ...
update
func Test_mStruct_vl1(t *testing.T) {
type fields struct {
info string
time time.Time
}
tests := []struct {
name string
fields fields
want bool
}{
{
name: "some test",
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,
}
if got := s.vl1(); got != tt.want {
t.Errorf("vl1() = %v, want %v", got, tt.want)
}
})
}
}

Answer 1

First you need a type (any type) that implements the vInterface interface. Here's a simple example:
type mockedVInterface struct {
value bool
}
func (m mockedVInterface) function1() bool {
return m.value
}
This is a simple enough implementation which we can control: we can tell what its function1() function should return by simply setting that value to its value field.
This mockedVInterface type is created solely for testing purposes, the production code does not need it. Put it in the same file where you have the test code (put it before Test_callSomething()).
And here's the testing code:
func Test_callSomething(t *testing.T) {
type args struct {
si vInterface
}
tests := []struct {
name string
args args
want bool
}{
{
name: "testing false",
args: args{
si: mockedVInterface{value: false},
},
want: false,
},
{
name: "testing true",
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)
}
})
}
}
Note that in this simple case we could also use a simple non-struct type that has bool as its underlying type like this:
type mockedVInterface bool
func (m mockedVInterface) function1() bool {
return bool(m)
}
And it works and testing code is also simpler:
tests := []struct {
name string
args args
want bool
}{
{
name: "testing false",
args: args{
si: mockedVInterface(false),
},
want: false,
},
{
name: "testing true",
args: args{
si: mockedVInterface(true),
},
want: true,
},
}
But this only works if the mockable interface has a single function with a single return value. In the general case a struct is needed.