Django Data Migration Test
Test utilities for easily testing Django data migrations
Installation
pip install django-test-data-migrations
Usage
Define the following functions in your migration file
data_forward(*args)-
data_backward(*args)(optional)
And then you can test the following way:
from django_test_data_migrations import DataMigrationsTestCaseBase
from app_a.models import Animal
class YourDataMigrationTestCase(DataMigrationsTestCaseBase):
def test__forward_migration__something_important(self):
# Prepare some data
# Run
self.data_forward(some_arg_0, some_arg_1, ...)
# Some assertions
def test__backward_migration__something_important(self):
# Prepare some data
# Run
self.data_backward(some_arg_0, some_arg_1, ...)
# Some assertionsExample
Say you have a simple Django project with following general structure
test_project/
└── app_a
  ├── apps.py
  ├── __init__.py
  ├── migrations
  │  ├── 0001_initial.py
  │  ├── 0002_datafix_addsuffixtoname.py
  │  └── __init__.py
  ├── models.py
  └── tests
  ├── __init__.py
  └── test_0002_datafix_addsuffixtoname.pywith the following model
from django.db import models
class Animal(models.Model):
species = models.CharField(blank=False, null=False, max_length=50)
name = models.CharField(blank=False, null=False, max_length=100)
def __str__(self):
return f"Animal [name={self.name}, species={self.species}]"along with the following migration
# app_a/migrations/0002_datafix_addsuffixtoname.py
from django.db import migrations
def data_forward(Animal, suffix):
for animal in Animal.objects.all():
animal.name += suffix
animal.save()
def data_backward(Animal, suffix):
for animal in Animal.objects.filter(name__endswith=suffix):
animal.name = animal.name.rstrip(suffix)
animal.save()
def forward(apps, schema_editor):
suffix = ' ZZ'
Animal = apps.get_model("app_a", "Animal")
data_forward(Animal, suffix)
def backward(apps, schema_editor):
suffix = ' ZZ'
Animal = apps.get_model("app_a", "Animal")
data_backward(Animal, suffix)
class Migration(migrations.Migration):
dependencies = [
('app_a', '0001_initial'),
]
operations = [
migrations.RunPython(forward, backward),
]You can test it as the following
from django_test_data_migrations import DataMigrationsTestCaseBase
from app_a.models import Animal
class DataMigrationsTestCase(DataMigrationsTestCaseBase):
app_name = "app_a"
migration_name = "0002_datafix_addsuffixtoname"
def test__data_forward__append_suffix_to_name(self):
# Prepare data before migration
dog = Animal.objects.create(name="Dog", species="dog")
cat = Animal.objects.create(name="Cat", species="cat")
# Run `data_forward` aka the entry point to your data migration
self.data_forward(Animal)
# Make your assertions
self.assertEqual(Animal.objects.get(id=dog.id).name, "Dog ZZ")
self.assertEqual(Animal.objects.get(id=cat.id).name, "Cat ZZ")
def test__data_backward__append_suffix_to_name(self):
dog = Animal.objects.create(name="Dog ZZ", species="dog")
cat = Animal.objects.create(name="Cat zz", species="cat")
self.data_backward(Animal)
self.assertEqual(Animal.objects.get(id=dog.id).name, "Dog")
self.assertEqual(Animal.objects.get(id=cat.id).name, "Cat zz")Why would you need this library?
- It runs your data migration test very fast.
- It encourages developers to write data-related Django migrations separately from model definition related Django migrations
- Writing tests for data related migrations is extremely important, but it's either tricky to do or very run-time consuming. This library intends to enable testing data migrations easy and fast
Development
Setup
Check requirements
poetry --version
Clone source code repository
git clone git@github.com:imranariffin/django-test-data-migrations.gitInstall dev dependencies
poetry installRun tests
make testYou should be ready to start development
