Golang standart library test example

power.go

package power

import "errors"

var NegativeError = errors.New("Negative component is not supported")

func power(base, i int) int {
	if i == 0 {
		return 1
	}
	if i % 2 == 0 {
		tmp := power(base, i / 2)
		return tmp * tmp
	} else {
		return base * power(base, i - 1)
	}
}

func Power(base, exponent int) (int, error) {
	if exponent < 0 {
		return -1, NegativeError
	}
	return power(base, exponent), nil
}

power_test.go

package power

import "testing"

func TestPower(t *testing.T) {
	for _, tc := range []struct{
		message string
		base int
		exponent int
		result int
		error error
	}{
		{"Positive base and exp", 2, 10,1024, nil},
		{"n^1 == n", 2, 1, 2, nil},
		{"n^0 == 1", 2,0,1,nil},
		{"Negative base", -2, 3, -8, nil},
		{"Negative exponent", 2, -1, -1, NegativeError},
	} {
		r, err := Power(tc.base, tc.exponent)
		if err != tc.error {
			t.Errorf("%s test failed. Expected error: %s; Actual: %s", tc.message, tc.error, err)
		}
		if r != tc.result {
			t.Errorf("%s test failed. Expected: %d; Actual: %d", tc.message, tc.result, r)
		}
	}
}