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Integration testing

Integration tests focus on testing how separate parts of the program work together. In the context of applications using a database, integration tests usually require a database to be available and contain data that is convenient to the scenarios intended to be tested.

One way to simulate a real world environment is to use Docker to encapsulate a database and some test data. This can be spun up and torn down with the tests and so operate as an isolated environment away from your production databases.

Note: This blog post offers a comprehensive guide on setting up an integration testing environment and writing integration tests against a real database, providing valuable insights for those looking to explore this topic.

Prerequisites

This guide assumes you have Docker and Docker Compose installed on your machine as well as Jest setup in your project.

The following ecommerce schema will be used throughout the guide. This varies from the traditional User and Post models used in other parts of the docs, mainly because it is unlikely you will be running integration tests against your blog.

Ecommerce schema
schema.prisma
// Can have 1 customer
// Can have many order details
model CustomerOrder {
id Int @id @default(autoincrement())
createdAt DateTime @default(now())
customer Customer @relation(fields: [customerId], references: [id])
customerId Int
orderDetails OrderDetails[]
}

// Can have 1 order
// Can have many products
model OrderDetails {
id Int @id @default(autoincrement())
products Product @relation(fields: [productId], references: [id])
productId Int
order CustomerOrder @relation(fields: [orderId], references: [id])
orderId Int
total Decimal
quantity Int
}

// Can have many order details
// Can have 1 category
model Product {
id Int @id @default(autoincrement())
name String
description String
price Decimal
sku Int
orderDetails OrderDetails[]
category Category @relation(fields: [categoryId], references: [id])
categoryId Int
}

// Can have many products
model Category {
id Int @id @default(autoincrement())
name String
products Product[]
}

// Can have many orders
model Customer {
id Int @id @default(autoincrement())
email String @unique
address String?
name String?
orders CustomerOrder[]
}

The guide uses a singleton pattern for Prisma Client setup. Refer to the singleton docs for a walk through of how to set that up.

Add Docker to your project

Docker compose code pointing towards image of container holding a Postgres database

With Docker and Docker compose both installed on your machine you can use them in your project.

  1. Begin by creating a docker-compose.yml file at your projects root. Here you will add a Postgres image and specify the environments credentials.
docker-compose.yml
# Set the version of docker compose to use
version: '3.9'

# The containers that compose the project
services:
db:
image: postgres:13
restart: always
container_name: integration-tests-prisma
ports:
- '5433:5432'
environment:
POSTGRES_USER: prisma
POSTGRES_PASSWORD: prisma
POSTGRES_DB: tests

Note: The compose version used here (3.9) is the latest at the time of writing, if you are following along be sure to use the same version for consistency.

The docker-compose.yml file defines the following:

  • The Postgres image (postgres) and version tag (:13). This will be downloaded if you do not have it locally available.
  • The port 5433 is mapped to the internal (Postgres default) port 5432. This will be the port number the database is exposed on externally.
  • The database user credentials are set and the database given a name.
  1. To connect to the database in the container, create a new connection string with the credentials defined in the docker-compose.yml file. For example:
.env.test
DATABASE_URL="postgresql://prisma:prisma@localhost:5433/tests"
info

The above .env.test file is used as part of a multiple .env file setup. Checkout the using multiple .env files. section to learn more about setting up your project with multiple .env files

  1. To create the container in a detached state so that you can continue to use the terminal tab, run the following command:
docker-compose up -d
  1. Next you can check that the database has been created by executing a psql command inside the container. Make a note of the container id.

    docker ps
    Show CLI results

Note: The container id is unique to each container, you will see a different id displayed.

  1. Using the container id from the previous step, run psql in the container, login with the created user and check the database is created:

    docker exec -it 1322e42d833f psql -U prisma tests
    Show CLI results

Integration testing

Integration tests will be run against a database in a dedicated test environment instead of the production or development environments.

The flow of operations

The flow for running said tests goes as follows:

  1. Start the container and create the database
  2. Migrate the schema
  3. Run the tests
  4. Destroy the container

Each test suite will seed the database before all the test are run. After all the tests in the suite have finished, the data from all the tables will be dropped and the connection terminated.

The function to test

The ecommerce application you are testing has a function which creates an order. This function does the following:

  • Accepts input about the customer making the order
  • Accepts input about the product being ordered
  • Checks if the customer has an existing account
  • Checks if the product is in stock
  • Returns an "Out of stock" message if the product doesn't exist
  • Creates an account if the customer doesn't exist in the database
  • Create the order

An example of how such a function might look can be seen below:

create-order.ts
import prisma from '../client'

export interface Customer {
id?: number
name?: string
email: string
address?: string
}

export interface OrderInput {
customer: Customer
productId: number
quantity: number
}

/**
* Creates an order with customer.
* @param input The order parameters
*/
export async function createOrder(input: OrderInput) {
const { productId, quantity, customer } = input
const { name, email, address } = customer

// Get the product
const product = await prisma.product.findUnique({
where: {
id: productId,
},
})

// If the product is null its out of stock, return error.
if (!product) return new Error('Out of stock')

// If the customer is new then create the record, otherwise connect via their unique email
await prisma.customerOrder.create({
data: {
customer: {
connectOrCreate: {
create: {
name,
email,
address,
},
where: {
email,
},
},
},
orderDetails: {
create: {
total: product.price,
quantity,
products: {
connect: {
id: product.id,
},
},
},
},
},
})
}

The test suite

The following tests will check if the createOrder function works as it should do. They will test:

  • Creating a new order with a new customer
  • Creating an order with an existing customer
  • Show an "Out of stock" error message if a product doesn't exist

Before the test suite is run the database is seeded with data. After the test suite has finished a deleteMany is used to clear the database of its data.

tip

Using deleteMany may suffice in situations where you know ahead of time how your schema is structured. This is because the operations need to be executed in the correct order according to how the model relations are setup.

However, this doesn't scale as well as having a more generic solution that maps over your models and performs a truncate on them. For those scenarios and examples of using raw SQL queries see Deleting all data with raw SQL / TRUNCATE

__tests__/create-order.ts
import prisma from '../src/client'
import { createOrder, Customer, OrderInput } from '../src/functions/index'

beforeAll(async () => {
// create product categories
await prisma.category.createMany({
data: [{ name: 'Wand' }, { name: 'Broomstick' }],
})

console.log('✨ 2 categories successfully created!')

// create products
await prisma.product.createMany({
data: [
{
name: 'Holly, 11", phoenix feather',
description: 'Harry Potters wand',
price: 100,
sku: 1,
categoryId: 1,
},
{
name: 'Nimbus 2000',
description: 'Harry Potters broom',
price: 500,
sku: 2,
categoryId: 2,
},
],
})

console.log('✨ 2 products successfully created!')

// create the customer
await prisma.customer.create({
data: {
name: 'Harry Potter',
email: '[email protected]',
address: '4 Privet Drive',
},
})

console.log('✨ 1 customer successfully created!')
})

afterAll(async () => {
const deleteOrderDetails = prisma.orderDetails.deleteMany()
const deleteProduct = prisma.product.deleteMany()
const deleteCategory = prisma.category.deleteMany()
const deleteCustomerOrder = prisma.customerOrder.deleteMany()
const deleteCustomer = prisma.customer.deleteMany()

await prisma.$transaction([
deleteOrderDetails,
deleteProduct,
deleteCategory,
deleteCustomerOrder,
deleteCustomer,
])

await prisma.$disconnect()
})

it('should create 1 new customer with 1 order', async () => {
// The new customers details
const customer: Customer = {
id: 2,
name: 'Hermione Granger',
email: '[email protected]',
address: '2 Hampstead Heath',
}
// The new orders details
const order: OrderInput = {
customer,
productId: 1,
quantity: 1,
}

// Create the order and customer
await createOrder(order)

// Check if the new customer was created by filtering on unique email field
const newCustomer = await prisma.customer.findUnique({
where: {
email: customer.email,
},
})

// Check if the new order was created by filtering on unique email field of the customer
const newOrder = await prisma.customerOrder.findFirst({
where: {
customer: {
email: customer.email,
},
},
})

// Expect the new customer to have been created and match the input
expect(newCustomer).toEqual(customer)
// Expect the new order to have been created and contain the new customer
expect(newOrder).toHaveProperty('customerId', 2)
})

it('should create 1 order with an existing customer', async () => {
// The existing customers email
const customer: Customer = {
email: '[email protected]',
}
// The new orders details
const order: OrderInput = {
customer,
productId: 1,
quantity: 1,
}

// Create the order and connect the existing customer
await createOrder(order)

// Check if the new order was created by filtering on unique email field of the customer
const newOrder = await prisma.customerOrder.findFirst({
where: {
customer: {
email: customer.email,
},
},
})

// Expect the new order to have been created and contain the existing customer with an id of 1 (Harry Potter from the seed script)
expect(newOrder).toHaveProperty('customerId', 1)
})

it("should show 'Out of stock' message if productId doesn't exit", async () => {
// The existing customers email
const customer: Customer = {
email: '[email protected]',
}
// The new orders details
const order: OrderInput = {
customer,
productId: 3,
quantity: 1,
}

// The productId supplied doesn't exit so the function should return an "Out of stock" message
await expect(createOrder(order)).resolves.toEqual(new Error('Out of stock'))
})

Running the tests

This setup isolates a real world scenario so that you can test your applications functionality against real data in a controlled environment.

You can add some scripts to your projects package.json file which will setup the database and run the tests, then afterwards manually destroy the container.

package.json
  "scripts": {
"docker:up": "docker-compose up -d",
"docker:down": "docker-compose down",
"test": "yarn docker:up && yarn prisma migrate deploy && jest -i"
},

The test script does the following:

  1. Runs docker-compose up -d to create the container with the Postgres image and database.
  2. Applies the migrations found in ./prisma/migrations/ directory to the database, this creates the tables in the container's database.
  3. Executes the tests.

Once you are satisfied you can run yarn docker:down to destroy the container, its database and any test data.