An idea for Go template mocking/output recording

htmlTemplateMock.go

/*
Basically, while writing a web app in Go I felt that
templates were the most undertested part of it.
I have no checks whether a handler actually executes a template,
is it the right one, is the correct context passed, etc.

This kind of mock provides a way to make lots of these checks.
*/

type Executable interface{
	Execute(wr io.Writer, data interface{}) error
	ExecuteTemplate(wr io.Writer, name string, data interface{}) error
}

// Your template map (instead of map[string]*template.Template)
// html/template or text/template templates satisfy Executable automatically.
var templates map[string]Executable

// This wraps the real template
type TemplateMock struct {
	*template.Template
	
	// some private fields
}

// Satisfies Executable
func (t *TemplateMock) Execute(wr io.Writer, data interface{}) error
func (t *TemplateMock) ExecuteTemplate(wr io.Writer, name string, data interface{}) error

// But has benefits for testing, like:
func (t *TemplateMock) TimesRendered() int
func (t *TemplateMock) Output() []byte
func (t *TemplateMock) ContextReceived() interface{}
// Probably some more.

// In production
templates["index.html"] = template.ParseFiles(...)

// In tests
templates["index.html"] = &TemplateMock{template.ParseFiles(...)}