Mutation testing example

example.go

// Data represents some arbitrary thing in the universe.
type Data struct {
 prices  []int
 checked bool
}
// Moon? returns true if the price is indicative of the thing going to the moon.
func Moon(data *Data) bool {
 // Is the next line important?
 // Would any test fail if this line were mutated to
 // _ = true ?
 data.checked = true
 if data.prices[0] > 0 {
  return true
 }
 return false
}
// TestMoon covers 100% lines of code, but it doesn't test any side effects such
// as the one on line 15.
func TestMoon(t *testing.T) {
 tests := []struct {
  data *Data
  want bool
 }{
  {
   data: &Data{prices: []int{0}},
   want: false,
  },
  {
   data: &Data{prices: []int{1}},
   want: true,
  },
 }
 for _, tt := range tests {
  got := Moon(tt.data)
  if got != tt.want {
   t.Errorf("Moon(%+v) = %t, wanted %t", tt.data, got, tt.want)
  }
 }
}