Testing code with timers in Go in a 100% deterministic manner, without relying on time passing

foo.go

package main

import (
	"fmt"
	"time"
)

type Foo struct {
	t *time.Ticker
}

func NewFoo() *Foo {
	return &Foo{
		t: time.NewTicker(time.Second),
	}
}

func (f *Foo) Run() {
	for range f.t.C {
		fmt.Println("tick!")
	}
}

foo_test.go

package main

import (
	"testing"
	"time"
)

func TestFooOnce(t *testing.T) {
	f := NewFoo()
	myticker := make(chan time.Time, 1)
	// the "C" attribute is a receive-only chan so we need to use a local
	// variable as the writing end.
	f.t.C = myticker
	myticker <- time.Time{}
	close(myticker)
	f.Run()
}

func TestFooTwice(t *testing.T) {
	f := NewFoo()
	myticker := make(chan time.Time, 2)
	f.t.C = myticker
	myticker <- time.Time{}
	myticker <- time.Time{}
	close(myticker)
	f.Run()
}