exemplo interface e testes #golang

main.go

package main

import (
	"fmt"
)

type contrato interface {
	Insert() string
}

type impl struct {
}

func (i impl) Insert() string {
	return "inserido"
}

func execInsert(c contrato) string {
	return c.Insert()
}

func main() {
	aa := impl{}
	fmt.Printf("Insert: %s", execInsert(aa))
}

main_test.go

package main

import (
	"testing"
)

type contratoMock struct{}

func (c contratoMock) Insert() string {
	return "mock"
}
func Test_execInsert(t *testing.T) {
	tests := []struct {
		name string
		args contrato
	}{
		{name: "a", args: contratoMock{}},
	}
	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			execInsert(tt.args)
		})
	}
}