Introduction to testing in Go

At the end of a working day, a tired programmer wrote test cases for simple calculator program code. Everything is fine with the func calc code, but something is clearly wrong with the tests.

code:

package simpleCalc

func calc(a, b int, op string) (int, bool) {
	switch op {
	case "+":
		return a + b, true
	case "-":
		return a - b, true
	case "*":
		return a * b, true
	case "/":
		if b == 0 {
			return 0, false
		}
		return a / b, true
	default:
		return 0, false
	}
}

tests:

package simpleCalc

import "testing"

func TestMul(t *testing.T) {
	expected := 20
	got, ok := calc(4, 5, "*")
	if got != expected || !ok {
		t.Errorf("expected: %v, got: %v", expected, got)
	}
}

func TestDiv(t *testing.T) {
	expected := 7
	got, ok := calc(49, 7, "/")
	if got != expected || !ok {
		t.Errorf("expected: %v, got: %v", expected, got)
	}
}

func TestDivZero(t *testing.T) {
	expected := 0
	got, ok := calc(49, 0, "/")
	if got != expected || !ok {
		t.Errorf("expected: %v, got: %v", expected, got)
	}
}

func TestDefault(t *testing.T) {
	expected := 0
	got, ok := calc(49, 7, "#")
	if got != expected || !ok {
		t.Errorf("expected: %v, got: %v", expected, got)
	}
}

Which test cases will fail?