You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: error_test.go
    path of file: ./repos/bud/internal/once
    
    the code of the file until where you have to start completion: package once_test

import (
	"errors"
	"testing"

	"github.com/livebud/bud/internal/is"
	"github.com/livebud/bud/internal/once"
)

func TestErrorNil(t *testing.T) {
	is := is.New(t)
	var once once.Error
	called := 0
	err := once.Do(func() error {
		called++
		return nil
	})
	is.NoErr(err)
	
    
func TestError(t *testing.T) {
	is := is.New(t)
	var once once.Error
	called := 0
	err := once.Do(func() error {
		called++
		return errors.New("oh noz")
	})
	is.True(err != nil)
	is.Equal(err.Error(), "oh noz")
	is.Equal(called, 1)
	err = once.Do(func() error {
		called++
		return err
	})
	is.True(err != nil)
	is.Equal(err.Error(), "oh noz")
	is.Equal(called, 1)
}