Golang how to write clean testable code in golang with this simple example

This is a simplified example based off of a small personal project, but I'm having trouble designing something like this at a larger scale in clean testable go code. I'm feeling completely hamstrung without constructors, inheritance, and the like. Everything I've found so far has been either a trivial example or wildly complex, so I'm struggling to put this together.

The PopulateLibrary() function will be called in parallel using a waitGroup, to insert 50 books in parallel.

// struct that book inserter API accepts
type InsertBookTemplate struct {
  name      string
  genre     string
  subGenre  string
  type      string
  authorBio AuthorBio
  chapters  []*Chapter{}
}

type AuthorBio struct {
 bio   string
 school string
}

type Chapter struct {
  name        string
  description string
}

// to be called in parallel with waitGroups
func PopulateLibrary(title, genre, author, publisher, description, language string) string {

// set some default vars that all books use
subGenre := getSubGenre(genre, author)
authorBio, authorSchool := getAuthorInfo(author, publisher)
publisher := "Published by: " + publisher
translations := translationsAvailable(language)
type := "hardcover"

numChapters := 10

//override defaults per genre
switch genre{
case "standard":
  
case "cooking":
  translations = ""
case "math":
  translations = ""
  numChapters = 20
case "sci-fi":
  translations = "spanish german"
  type = "softcover"
  if subGenre == "" {
    subGenre = "new sci-fi"
  } else {
    subGenre = "cyberpunk"
  }
case "horror":
  translations = "Spanish"
case "child":
  numChapters = 3
}

newBook := &InsertBookTemplate{}
newBook.name = title
nweBook.genre = genre
newBook.subGenre = subGenre
newBook.type = type

newAuthorBio := &authorBio{}
newAuthorBio.bio = authorBio
newAuthorBio.school = authorSchool
newBook.authorBio = newAuthorBio

chapters := []*Chapter{}
for i:=0; i <= numChapters; i++ {
  chapter := &Chapter{}
  chapter.name = getSomeName(i)
  chapter.description = getSomeDescription(i)
  chapters = append(chapters, chapter)
}

newBook.chapters := []*Chapter{}
newBook.chapters := append(newBook.chapters, chapters...)

InsertNewBook(newBook)

}