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: parallel.go
    path of file: ./repos/gnomock
    
    the code of the file until where you have to start completion: package gnomock

import "golang.org/x/sync/errgroup"

// InParallel begins parallel preset execution setup. Use Start to add more
// presets with their configuration to parallel execution, and G
    
func (b *Parallel) Go() ([]*Container, error) {
	var g errgroup.Group

	containers := make([]*Container, len(b.presets))

	for i, preset := range b.presets {
		containerIndex := i
		p := preset

		g.Go(func() error {
			c, err := Start(p.Preset, p.opts...)
			containers[containerIndex] = c

			return err
		})
	}

	return containers, g.Wait()
}