Go interfaces and test cases

calculate_test.go

package main

import "testing"

type calculateTest struct {
	arg1, arg2, expectedResult int
}

var addTests = []calculateTest{
	{2, 3, 5},
	{4, 8, 12},
	{6, 9, 14},
	{3, 10, 13},
}

var subtractTests = []calculateTest{
	{2, 3, -1},
	{4, 8, -4},
	{9, 6, 3},
	{13, 10, 3},
}

func TestAdd(t *testing.T) {

	for _, test := range addTests {
		var calculate Calculate

		calculate = &InputNumbers{
			FirstNumber:  test.arg1,
			SecondNumber: test.arg2,
		}
		result := calculate.Add()
		if result != test.expectedResult {
			t.Errorf("Output %d not equal to expected %d", result, test.expectedResult)
		}
	}
}

func TestSubtract(t *testing.T) {

	for _, test := range subtractTests {
		var calculate Calculate

		calculate = &InputNumbers{
			FirstNumber:  test.arg1,
			SecondNumber: test.arg2,
		}
		result := calculate.Subtract()
		if result != test.expectedResult {
			t.Errorf("Output %d not equal to expected %d", result, test.expectedResult)
		}
	}
}

main.go

package main

import (
	"fmt"
)

type Calculate interface {
	Add() int
	Subtract() int
	Multiply() int
}

type InputNumbers struct {
	FirstNumber  int
	SecondNumber int
}

func (i *InputNumbers) Add() int {
	return i.FirstNumber + i.SecondNumber
}

func (i *InputNumbers) Subtract() int {
	return i.FirstNumber - i.SecondNumber
}

func (i *InputNumbers) Multiply() int {
	return i.FirstNumber * i.SecondNumber
}

func main() {

	var result Calculate

	result = &InputNumbers{
		FirstNumber:  10,
		SecondNumber: 5,
	}

	add := result.Add()
	subtract := result.Subtract()
	multiply := result.Multiply()

	fmt.Printf("Result for the Calculate operations is Add: %d, Subtract: %d, Multiply: %d", add, subtract, multiply)

}

The result of test cases are:
=== RUN TestAdd
add_test.go:34: Output 15 not equal to expected 14
--- FAIL: TestAdd (0.00s)
=== RUN TestSubtract
--- PASS: TestSubtract (0.00s)
FAIL
exit status 1
FAIL _/Users/amit.das/Desktop/test-cases 1.619s

The test TestAdd has failed since one of the results is incorrect.
Test TestSubtract has passed since all the test cases are valid.