data     = `<baz>`
		want     = `&lt;baz&gt;`
	)
	// Templates "foo" and "bar" both alias the same underlying parse tree.
	tpl := Must(New("foo").Parse(tmplText))
	if _, err := tpl.AddParseTree("bar", tpl.Tree); err != nil {
		t.Fatalf("AddParseTree error: %v", err)
	}
	var b1, b2 strings.Builder
	if err := tpl.ExecuteTemplate(&b1, "foo", data); err != nil {
		t.Fatalf(`ExecuteTemplate failed for "foo": %v`, err)
	}

	}
	// Add a non-empty template to check that the error is helpful.
	tests, err := New("").Parse(testTemplates)
	if err != nil {
		t.Fatal(err)
	}
	tmpl.AddParseTree("secondary", tests.Tree)
	err = tmpl.Execute(&b, 0)
	if err == nil {
		t.Fatal("expected second error")
	}
	got = err.Error()
	want = `template: empty: "empty" is an incomplete or empty template`

	}

	// Add a non-empty template to check that the error is helpful.
	tmpl = New("empty")
	tests, err := New("").Parse(testTemplates)
	if err != nil {
		t.Fatal(err)
	}
	tmpl.AddParseTree("secondary", tests.Tree)
	err = tmpl.Execute(&b, 0)
	if err == nil {
		t.Fatal("expected second error")
	}
	got = err.Error()
	if got != want {
		t.Errorf("expected error %s got %s", want, got)