How To Write Integration Tests in NestJS?

Integration testing is an important part of software development, ensuring that various parts of your application work together as expected. In NestJS, integration testing allows you to test the interaction between different modules, services, and controllers.

In this article, we will guide you through the process of writing integration tests in NestJS, covering essential concepts, tools, and examples to help you implement robust tests for your application.

What are Integration Tests?

Integration testing is the phase in software testing where individual components or systems are combined and tested as a group. Unlike unit testing, which focuses on testing isolated components in isolation, integration testing ensures that these components work together as expected.

In NestJS, integration tests typically involve testing how modules, controllers, services, and external resources (like databases and APIs) interact. It ensures that your application performs correctly under real-world conditions.

Steps To Write Integration Tests in NestJS

Step 1: Set Up Your Testing Environment

npm i -g @nestjs/cli
nest new project-name

Step 2: Create the Patient and Appointment Modules

nest g module patient
nest g module appointment

Step 3: Create the Services and Controllers

nest g service patient
nest g controller patient
nest g service appointment
nest g controller appointment

Folder Structure

Dependencies

"dependencies": {
 "@nestjs/common": "^10.0.0",
 "@nestjs/core": "^10.0.0",
 "@nestjs/platform-express": "^10.0.0",
 "reflect-metadata": "^0.2.0",
 "rxjs": "^7.8.1"
 },
"devDependencies": {
 "@nestjs/cli": "^10.0.0",
 "@nestjs/schematics": "^10.0.0",
 "@nestjs/testing": "^10.0.0",
 "@types/express": "^4.17.17",
 "@types/jest": "^29.5.2",
 "@types/node": "^20.3.1",
 "@types/supertest": "^6.0.0",
 "@typescript-eslint/eslint-plugin": "^7.0.0",
 "@typescript-eslint/parser": "^7.0.0",
 "eslint": "^8.42.0",
 "eslint-config-prettier": "^9.0.0",
 "eslint-plugin-prettier": "^5.0.0",
 "jest": "^29.5.0",
 "prettier": "^3.0.0",
 "source-map-support": "^0.5.21",
 "supertest": "^7.0.0",
 "ts-jest": "^29.1.0",
 "ts-loader": "^9.4.3",
 "ts-node": "^10.9.1",
 "tsconfig-paths": "^4.2.0",
 "typescript": "^5.1.3"
 },

Step 4: Write Integration Tests

Create a test file for your appointment module

appointment.model.ts
appointment.module.ts
appointment.service.spec.ts
appointment.service.ts

Create a test file for your patient module

patient.model.ts
patient.modules.ts
patient.service.spec.ts
patient.service.ts

Create a app files in src folder

app.controller.spec.ts
app.controller.ts
app.module.ts
app.service.ts
main.ts

Create a new Test folder with this file inside

app.e2e-spec.ts

Step 5: Start and Run the Test

npm start test

Run the test using the following command

npm test --