Mocked method not working in golang while running the test cases

[prakash sharma]

Need help:

https://stackoverflow.com/questions/59693971/mocked-method-not-working-in-golang-while-running-the-test-cases

I am trying to mock an struct method in test cases but it is not working. I want to mock Validate method here: 

package main

import (
    "fmt"
)

type DemoInterface interface {
    Inc(int) (int, error)
    Validate(int) error
}
type DemoStruct struct{}

func (l DemoStruct) Inc(num int) (int, error) {
    err := l.Validate(num)
    if err != nil {
        return 0, err
    }
    num = num + 100
    return num, nil

}
func (l DemoStruct) Validate(num int) error {// SOME DB LOGIC IS HERE WHICH I CAN NOT POST at Stackoverflow
    if num > 100 {
        return fmt.Errorf("INVALID NUM %v", num)
    }
    return nil
}

func main() {
    s, err := DemoStruct{}.Inc(10)
    if err != nil {
        fmt.Println(err)
    }
    fmt.Println(s)

}

My test cases:

package main

import (
    "fmt"
    "testing"
)

const (
    SUCCESS = "SUCCESS"
    ERROR   = "ERROR"
)

type MockDemoStruct struct {
    DemoStruct
    functionality string
}

func (m MockDemoStruct) Validate(num int) error {
    switch m.functionality {
    case SUCCESS:
        return nil
    case ERROR:
        fmt.Errorf("MOCK ERROR %v", num)

    }
    return fmt.Errorf("MOCK ERROR %v", num)
}

func TestPath(t *testing.T) {

    t.Run("ERROR", func(t *testing.T) {
        ls := MockDemoStruct{DemoStruct{}, SUCCESS}
        res, err := ls.Inc(110)
        expected := fmt.Errorf("MOCK ERROR %v", 10)
        if err != expected {
            t.Errorf("NOT MATCH  %v  %v", err, expected)
            //-----------------NOT MATCH  INVALID NUM 110  MOCK ERROR 10 ERROR-----------------------------

        }
        fmt.Println(res)
    })
}

[Chris Burkert]

You could inject your dependencies. There is a funny talk by Liron Levin [1] which helped me a lot.

1: https://youtu.be/_B_vCEiO4mA

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[prakash sharma]

Thanks for your help Chris

Introduced dependency injection in this code using Delegation Design pattern with the help of interface.

Here's the details explanation

https://stackoverflow.com/a/59704965/5133838

Please share yours feedback.