got := err.Error()
	if got != want {
		t.Errorf("expected\n%q\ngot\n%q", want, got)
	}
}

type CustomError struct{}

func (*CustomError) Error() string { return "heyo !" }

// Check that a custom error can be returned.
func TestExecError_CustomError(t *testing.T) {
	failingFunc := func() (string, error) {
		return "", &CustomError{}
	}
	tmpl := Must(New("top").Funcs(FuncMap{