To create your first test, let's introduce a bug into your Book model.

Say you have decided to create a custom method on your Book model to indicate whether the book has been published recently. Your Book model may look something like this:

import datetime 
from django.utils import timezone 
 
from django.db import models 
 
# ... # 
 
class Book(models.Model): 
    title = models.CharField(max_length=100) 
    authors = models.ManyToManyField(Author) 
    publisher = models.ForeignKey(Publisher) 
    publication_date = models.DateField() 
 
    def recent_publication(self): 
        return self.publication_date >= timezone.now().date() 
datetime.timedelta(weeks=8) 
 
    # ... # 
 

First we have imported two new modules: Python's datetime and timezone from django.utils. We need these modules to be able to do calculations with dates. Then we have added a custom method to the Book...