Unit Testing http.MultipartForm

I want to test my http method that takes a post request and stores the given files.

func DownloadFiles(w http.ResponseWriter, r *http.Request) {
    r.ParseMultipartForm(2097152) //2MB
    
    files := r.MultipartForm.File["documents"] //files of type []*multipart.FileHeader
    for _, handler := range files {            //handler of type *multipart.FileHeader
        file, err := handler.Open()            //file of type multipart.File
        ... //Do something with files
    }
    w.WriteHeader(http.StatusOK)
}

How can i prepare a valid http.Request that features multipart-formdata and calls the function?