Go unit test example: _test package suffix + multiple test cases

math.go

package math

import "errors"

var ErrCantDivideByZero = errors.New("can't divide by zero")

// divide cannot be tested directly
func divide(x, y float32) float32 {
	return x / y
}

// Divide is exported and will be tested
func Divide(x, y int) (int, error) {
	if y == 0 {
		return 0, ErrCantDivideByZero
	}
	return int(divide(float32(x), float32(y))), nil
}

math_test.go

package math_test // _test suffix is used to prevent private members direct tests

import (
	"log"
	"os"
	"testing"

	. "mynamespace/math" // dot import to use public symbols without a package name
)

func TestDivide(t *testing.T) {
	cases := []struct {
		name string
		x    int
		y    int
		res  int
		err  error
	}{
		{
			name: "integer dividable without reminder",
			x:    4,
			y:    2,
			res:  2,
		},
		{
			name: "integer dividable with reminder",
			x:    3,
			y:    2,
			res:  1,
		},
		{
			name: "divide by zero",
			x:    4,
			y:    0,
			err:  ErrCantDivideByZero,
		},
		{
			name: "Intentionally broken test case",
			x:    0,
			y:    0,
			res:  1,
			err:  nil,
		},
	}

	for _, tc := range cases {
		t.Run(tc.name, func(t *testing.T) {
			log.Print("before test")
			defer log.Print("after test")

			res, err := Divide(tc.x, tc.y)
			if err != tc.err {
				t.Errorf("error expected %v, got %v", tc.err, err)
			}
			if res != tc.res {
				t.Errorf("result expected %d, got %d", tc.res, res)
			}
		})
	}
}

// inits tests globally (package wide)
func TestMain(m *testing.M) {
	log.Print("setup all")
	code := m.Run()
	log.Print("teardown all")
	os.Exit(code)
}

Output:

2021/12/03 15:20:16 setup all
=== RUN   TestDivide
=== RUN   TestDivide/integer_dividable_without_reminder
2021/12/03 15:20:16 before test
2021/12/03 15:20:16 after test
=== RUN   TestDivide/integer_dividable_with_reminder
2021/12/03 15:20:16 before test
2021/12/03 15:20:16 after test
=== RUN   TestDivide/divide_by_zero
2021/12/03 15:20:16 before test
2021/12/03 15:20:16 after test
=== RUN   TestDivide/Intentionally_broken_test_case
2021/12/03 15:20:16 before test
    mult_test.go:53: error expected <nil>, got can't divide by zero
    mult_test.go:56: result expected 1, got 0
2021/12/03 15:20:16 after test
--- FAIL: TestDivide (0.00s)
    --- PASS: TestDivide/integer_dividable_without_reminder (0.00s)
    --- PASS: TestDivide/integer_dividable_with_reminder (0.00s)
    --- PASS: TestDivide/divide_by_zero (0.00s)
    --- FAIL: TestDivide/Intentionally_broken_test_case (0.00s)


FAIL
2021/12/03 15:20:16 teardown all