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Test utilities for easily testing Django data migrations

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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

  1. data_forward(*args)
  2. data_backward(*args) (optional)
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 assertions

Example

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.py

with 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

SUFFIX = " ZZ"


def data_forward(Animal):
    for animal in Animal.objects.all():
        animal.name += SUFFIX
        animal.save()


def data_backward(Animal):
    for animal in Animal.objects.filter(name__endswith=SUFFIX):
        animal.name = animal.name.rstrip(SUFFIX)
        animal.save()


def forward(apps, schema_editor):
    Animal = apps.get_model("app_a", "Animal")
    data_forward(Animal)


def backward(apps, schema_editor):
    Animal = apps.get_model("app_a", "Animal")
    data_backward(Animal)


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?

  1. It runs your data migration test very fast.
  2. It encourages developers to write data-related Django migrations separately from model definition related Django migrations
  3. 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.git

Install dev dependencies

poetry install

Run tests

make test

You should be ready to start development

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