Example of how to stub out time.Now

timestubs.go

package foo

import "time"

// in your main package
var timeNow = time.Now

// in the _test.go:
func init() {
	// Panic if any tests cause timeNow to be called without stubbing it out
	timeNow = func() time.Time {
		panic("now called without stub")
	}
}

func TestFoo() {
	// Restore to the panicky stub at the end of the test
	defer func(orig func() time.Time) {
		timeNow = orig
	}(timeNow)

	// We can now reassign timeNow to do whatever we want
	timeNow = func() time.Time {
		return time.Now().UTC()
	}

	timeNow()

	// ... as many times as we want
	timeNow = func() time.Time {
		return time.Time{}
	}

	timeNow()
}

This just gave me the insight I needed to tackle some tests in my current project where I am calling functions directly defined in another package. I just need to alias them with a func variable in my application and use the alias instead of the original function, then override it in the test.