Golang time testing pattern

struct.go

package str

func UnixTimestamp() int64 {
	return time.Now().Unix()
}

type FragmentCreator struct {
	slug string

	// timeNowUnix is only used in testing to override getting the current timestamp
	timestamp func() int64
}

func (f FragmentCreator) filename() string {
	filename := fmt.Sprintf("%d-%s.yaml", f.timestamp(), f.slug)
	return filename

}

struct_test.go

package str

func TestFilename(t *testing.T) {
	fc := FragmentCreator{
		slug: "foobar",
		timestamp: func() int64 { return 1647345675 },
	}

	expected := "1647345675-foobar.yaml"
	got := fc.filename()
	assert.Equal(t, expected, got)
}

var.go

package vr

type FragmentCreator struct {
	slug string
}

var timeNowUnix = time.Now().Unix

func filename(fc FragmentCreator) string {
	t := timeNowUnix()
	filename := fmt.Sprintf("%d-%s.yaml", t, fc.slug)
	return filename
}

var_test.go

package vr

func TestFilename(t *testing.T) {
	fc := FragmentCreator{
    slug: "foobar"
  }

	timeNowUnix = func() int64 {
		return 1647345675
	}

	expected := "1647345675-foobar.yaml"
	got := filename(fc)
	assert.Equal(t, expected, got)
}