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End to End API Testing with Docker

by JPNovember 12th, 2019

Too Long; Didn't Read

In this article you'll see how you can engineer tests for yourself with Docker. The example will cover a simple set of CRUD endpoints for users. It's more than enough to grasp the concept and apply to the more complex business logic of your API. It creates "containerized" versions of all the external parts we use. It is mocking but on the outside of our code. Our API thinks it is in a real physical environment. This is more valuable than knowing if your class somewhere in the middle of the app works OK or not.

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featured image - End to End API Testing with Docker

Testing is a pain in general. Some don't see the point. Some see it but think of it as an extra step slowing them down. Sometimes tests are there but very long to run or unstable. In this article you'll see how you can engineer tests for yourself with Docker.

We want fast, meaningful and reliable tests written and maintained with minimal effort. It means tests that are useful to you as a developer on a day-to-day basis. They should boost your productivity and improve the quality of your software. Having tests because everybody says "you should have tests" is no good if it slows you down.

Let's see how to achieve this with not that much effort.

The example we are going to test

In this article we are going to test an API built with Node/express and use chai/mocha for testing. I've chosen a JS'y stack because the code is super short and easy to read. The principles applied are valid for any tech stack. Keep reading even if Javascript makes you sick.

The example will cover a simple set of CRUD endpoints for users. It's more than enough to grasp the concept and apply to the more complex business logic of your API.

We are going to use a pretty standard environment for the API:

- A Postgres database

- A Redis cluster

- Our API will use other external APIs to do its job

Your API might need a different environment. The principles applied in this article will remain the same. You'll use different Docker base images to run whatever component you might need.

Why Docker? And in fact Docker Compose

This section is a lot of arguments in favour or using Docker for testing. You can skip it if you want to get to the technical part right away.

The painful alternatives

To test your API in a close to production environment you have two choices. You can mock the environment at code level or run the tests on a real server with the database etc. installed.

Mocking everything at code level clutters the code and configuration of our API. It is also often not very representative of how the API will behave in production. Running the thing in a real server is infrastructure heavy. It is a lot of setup and maintenance, and it does not scale. Having a shared database, you can run only 1 test at a time to ensure test runs do not interfere with each other.

Docker Compose allows us to get the best of both worlds. It creates "containerized" versions of all the external parts we use. It is mocking but on the outside of our code. Our API thinks it is in a real physical environment. Docker compose will also create an isolated network for all the containers for a given test run. This allows you to run several of them in parallel on your local computer or a CI host.

Overkill?

You might wonder if it isn't overkill to go end to end tests at all with Docker compose. What about just running unit tests instead?

For the last 10 years, large monolith applications are being split into smaller services (trending towards the buzzy "micro services"). A given API component relies on more external parts (infrastructure or other APIs). As services get smaller, integration with the infrastructure becomes a bigger part of the job. You should keep a small gap between your production and your development environments. Otherwise problems will arise when going for production deploy. By definition these problems appear at the worst possible moment. They will lead to rushed fixes, drops in quality, and frustration for the team. Nobody wants that.

You might wonder if end to end tests with Docker compose run longer than traditional unit tests. Not really. You'll see in the example below that we can easily keep the tests under 1 minute. At great benefits: the tests reflect the application behaviour in the real world. This is more valuable than knowing if your class somewhere in the middle of the app works OK or not. Also, if you don't have any tests right now, starting from end to end gives you great benefits for little effort. You'll know all stacks of the application work together for the most common scenarios. That's already something! From there you can always refine a strategy to unit tests critical parts of your application.

Our first test

Let’s start with the easiest part. Our API and the Postgres database. And let’s run a simple CRUD test. Once we have that framework in place, we can add more features both to our component and to the test.

Here is our minimal API with a GET/POST to create and list users:

const express = require('express');
const bodyParser = require('body-parser');
const cors = require('cors');

const config = require('./config');

const db = require('knex')({
  client: 'pg',
  connection: {
    host : config.db.host,
    user : config.db.user,
    password : config.db.password,
  },
});

const app = express();

app.use(bodyParser.urlencoded({ extended: false }));
app.use(bodyParser.json());
app.use(cors());

app.route('/api/users').post(async (req, res, next) => {
  try {
    const { email, firstname } = req.body;
    // ... validate inputs here ...
    const userData = { email, firstname };

    const result = await db('users').returning('id').insert(userData);
    const id = result[0];
    res.status(201).send({ id, ...userData });
  } catch (err) {
    console.log(`Error: Unable to create user: ${err.message}. ${err.stack}`);
    return next(err);
  }
});

app.route('/api/users').get((req, res, next) => {
  db('users')
  .select('id', 'email', 'firstname')
  .then(users => res.status(200).send(users))
  .catch(err => {
      console.log(`Unable to fetch users: ${err.message}. ${err.stack}`);
      return next(err);
  });
});

try {
  console.log("Starting web server...");

  const port = process.env.PORT || 8000;
  app.listen(port, () => console.log(`Server started on: ${port}`));
} catch(error) {
  console.error(error.stack);
}
```

Here are our tests written with chai. The tests create a new user and fetch it back.
You can see that the tests are not coupled in any way with the code of our API.
The `SERVER_URL` variable specifies the endpoint to test. It can be a local or a remote environment.

```javascript
const chai = require("chai");
const chaiHttp = require("chai-http");
const should = chai.should();

const SERVER_URL = process.env.APP_URL || "http://localhost:8000";

chai.use(chaiHttp);

const TEST_USER = {
  email: "[email protected]",
  firstname: "John"
};

let createdUserId;

describe("Users", () => {
  it("should create a new user", done => {
    chai
      .request(SERVER_URL)
      .post("/api/users")
      .send(TEST_USER)
      .end((err, res) => {
        if (err) done(err)
        res.should.have.status(201);
        res.should.be.json;
        res.body.should.be.a("object");
        res.body.should.have.property("id");
        done();
      });
  });

  it("should get the created user", done => {
    chai
      .request(SERVER_URL)
      .get("/api/users")
      .end((err, res) => {
        if (err) done(err)
        res.should.have.status(200);
        res.body.should.be.a("array");

        const user = res.body.pop();
        user.id.should.equal(createdUserId);
        user.email.should.equal(TEST_USER.email);
        user.firstname.should.equal(TEST_USER.firstname);
        done();
      });
  });
});

Good. Now to test our API let's define a Docker compose environment. A file called

docker-compose.yml

will describe the containers Docker needs to run.

version: '3.1'

services:
  db:
    image: postgres
    environment:
      POSTGRES_USER: john
      POSTGRES_PASSWORD: mysecretpassword
    expose:
      - 5432

  myapp:
    build: .
    image: myapp
    command: yarn start
    environment:
      APP_DB_HOST: db
      APP_DB_USER: john
      APP_DB_PASSWORD: mysecretpassword
    expose:
      - 8000
    depends_on:
      - db

  myapp-tests:
    image: myapp
    command: dockerize
        -wait tcp://db:5432 -wait tcp://myapp:8000 -timeout 10s
        bash -c "node db/init.js && yarn test"
    environment:
      APP_URL: http://myapp:8000
      APP_DB_HOST: db
      APP_DB_USER: john
      APP_DB_PASSWORD: mysecretpassword
    depends_on:
      - db
      - myapp

So what do we have here. There are 3 containers:

- db spins up a fresh instance of PostgreSQL. We use the public Postgres image from Docker Hub. We set the database username and password. We tell Docker to expose the port 5432 the database will listen to so other containers can connect

- myapp is the container that will run our API. The

build

command tells Docker to actually build the container image from our source. The rest is like the db container: environment variables and ports

- myapp-tests is the container that will execute our tests. It will use the same image that myapp because the code will already be there so there is not need to build it again. The command

node db/init.js && yarn test

ran on the container will initialize the database (create tables etc.) and run the tests. We use dockerize to wait for all the required servers to be up and running. The

depends_on

options will ensure that containers start in a certain order. It does not ensure that the database inside the db container is actually ready to accept connections. Nor that our API server is already up.

The definition of the environment is like 20 lines of very easy to understand code. The only brainy part is the environment definition. User names, passwords and URLs must be consistent so containers can actually work together.

One thing to notice is that Docker compose will set the host of the containers it creates to the name of the container. So the database won't be available under

localhost:5432

but

db:5432

. The same way our API will served under

myapp:8000

. There is no localhost of any kind here. This means that your API must support environment variables when it comes to environment definition. No hardcoded stuff. But that has nothing to do with Docker or this article. A configurable application is point 3 of the 12 factor app manifesto, so you should be doing it already.

The very last thing we need to tell Docker is how to actually build the container myapp. We use a Dockerfile like below. The content is specific to your tech stack but the idea is to bundle your API into a runnable server.

The example below for our Node API installs Dockerize, installs the API dependencies and copies the code of the API inside the container (the server is written in raw JS so no need to compile it).

FROM node AS base

# Dockerize is needed to sync containers startup
ENV DOCKERIZE_VERSION v0.6.0
RUN wget https://github.com/jwilder/dockerize/releases/download/$DOCKERIZE_VERSION/dockerize-alpine-linux-amd64-$DOCKERIZE_VERSION.tar.gz \
    && tar -C /usr/local/bin -xzvf dockerize-alpine-linux-amd64-$DOCKERIZE_VERSION.tar.gz \
    && rm dockerize-alpine-linux-amd64-$DOCKERIZE_VERSION.tar.gz

RUN mkdir -p ~/app

WORKDIR ~/app

COPY package.json .
COPY yarn.lock .

FROM base AS dependencies

RUN yarn

FROM dependencies AS runtime

COPY . .

Typically from the line

WORKDIR ~/app

and below you would run commands that would build your application.

And here is the command we use to run the tests:

docker-compose up --build --abort-on-container-exit

This command will tell Docker compose to spin up the components defined in our

docker-compose.yml

file. The

--build

flag will trigger the build of the myapp container by executing the content of the

Dockerfile

above. The

--abort-on-container-exit

will tell Docker compose to shutdown the environment as soon as one container exits. That works well since the only component meant to exit is the test container myapp-tests after the tests are executed. Cherry on the cake, the

docker-compose

command will exit with the same exit code as the container that triggered the exit. It means that we can check if the tests succeeded or not from the command line. This is very useful for automated builds in a CI environment.

Isn't that the perfect test setup?

The full example is here on GitHub.

You can clone the repository and run the docker compose command:

docker-compose up --build --abort-on-container-exit

Of course you need Docker installed. Docker has the troublesome tendency of forcing you to sign up for an account just to download the thing. But you actually don't have to. Go to the release notes (link for Windows and link for Mac) and download not the latest version but the one right before. This is a direct download link.

The very first run of the tests will be longer than usual. It is because Docker will have to download the base images for your containers and cache a few things. Next runs will be much faster.

Logs from the run will look as below. You can see that Docker is cool enough to put logs from all the components on the same timeline. This is very handy when looking for errors.

Creating tuto-api-e2e-testing_db_1    ... done
Creating tuto-api-e2e-testing_redis_1 ... done
Creating tuto-api-e2e-testing_myapp_1 ... done
Creating tuto-api-e2e-testing_myapp-tests_1 ... done
Attaching to tuto-api-e2e-testing_redis_1, tuto-api-e2e-testing_db_1, tuto-api-e2e-testing_myapp_1, tuto-api-e2e-testing_myapp-tests_1
db_1           | The files belonging to this database system will be owned by user "postgres".
redis_1        | 1:M 09 Nov 2019 21:57:22.161 * Running mode=standalone, port=6379.
myapp_1        | yarn run v1.19.0
redis_1        | 1:M 09 Nov 2019 21:57:22.162 # WARNING: The TCP backlog setting of 511 cannot be enforced because /proc/sys/net/core/somaxconn is set to the lower value of 128.
redis_1        | 1:M 09 Nov 2019 21:57:22.162 # Server initialized
db_1           | This user must also own the server process.
db_1           | 
db_1           | The database cluster will be initialized with locale "en_US.utf8".
db_1           | The default database encoding has accordingly been set to "UTF8".
db_1           | The default text search configuration will be set to "english".
db_1           | 
db_1           | Data page checksums are disabled.
db_1           | 
db_1           | fixing permissions on existing directory /var/lib/postgresql/data ... ok
db_1           | creating subdirectories ... ok
db_1           | selecting dynamic shared memory implementation ... posix
myapp-tests_1  | 2019/11/09 21:57:25 Waiting for: tcp://db:5432
myapp-tests_1  | 2019/11/09 21:57:25 Waiting for: tcp://redis:6379
myapp-tests_1  | 2019/11/09 21:57:25 Waiting for: tcp://myapp:8000
myapp_1        | $ node server.js
redis_1        | 1:M 09 Nov 2019 21:57:22.163 # WARNING you have Transparent Huge Pages (THP) support enabled in your kernel. This will create latency and memory usage issues with Redis. To fix this issue run the command 'echo never > /sys/kernel/mm/transparent_hugepage/enabled' as root, and add it to your /etc/rc.local in order to retain the setting after a reboot. Redis must be restarted after THP is disabled.
db_1           | selecting default max_connections ... 100
myapp_1        | Starting web server...
myapp-tests_1  | 2019/11/09 21:57:25 Connected to tcp://myapp:8000
myapp-tests_1  | 2019/11/09 21:57:25 Connected to tcp://db:5432
redis_1        | 1:M 09 Nov 2019 21:57:22.164 * Ready to accept connections
myapp-tests_1  | 2019/11/09 21:57:25 Connected to tcp://redis:6379
myapp_1        | Server started on: 8000
db_1           | selecting default shared_buffers ... 128MB
db_1           | selecting default time zone ... Etc/UTC
db_1           | creating configuration files ... ok
db_1           | running bootstrap script ... ok
db_1           | performing post-bootstrap initialization ... ok
db_1           | syncing data to disk ... ok
db_1           | 
db_1           | 
db_1           | Success. You can now start the database server using:
db_1           | 
db_1           |     pg_ctl -D /var/lib/postgresql/data -l logfile start
db_1           | 
db_1           | initdb: warning: enabling "trust" authentication for local connections
db_1           | You can change this by editing pg_hba.conf or using the option -A, or
db_1           | --auth-local and --auth-host, the next time you run initdb.
db_1           | waiting for server to start....2019-11-09 21:57:24.328 UTC [41] LOG:  starting PostgreSQL 12.0 (Debian 12.0-2.pgdg100+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 8.3.0-6) 8.3.0, 64-bit
db_1           | 2019-11-09 21:57:24.346 UTC [41] LOG:  listening on Unix socket "/var/run/postgresql/.s.PGSQL.5432"
db_1           | 2019-11-09 21:57:24.373 UTC [42] LOG:  database system was shut down at 2019-11-09 21:57:23 UTC
db_1           | 2019-11-09 21:57:24.383 UTC [41] LOG:  database system is ready to accept connections
db_1           |  done
db_1           | server started
db_1           | CREATE DATABASE
db_1           | 
db_1           | 
db_1           | /usr/local/bin/docker-entrypoint.sh: ignoring /docker-entrypoint-initdb.d/*
db_1           | 
db_1           | waiting for server to shut down....2019-11-09 21:57:24.907 UTC [41] LOG:  received fast shutdown request
db_1           | 2019-11-09 21:57:24.909 UTC [41] LOG:  aborting any active transactions
db_1           | 2019-11-09 21:57:24.914 UTC [41] LOG:  background worker "logical replication launcher" (PID 48) exited with exit code 1
db_1           | 2019-11-09 21:57:24.914 UTC [43] LOG:  shutting down
db_1           | 2019-11-09 21:57:24.930 UTC [41] LOG:  database system is shut down
db_1           |  done
db_1           | server stopped
db_1           | 
db_1           | PostgreSQL init process complete; ready for start up.
db_1           | 
db_1           | 2019-11-09 21:57:25.038 UTC [1] LOG:  starting PostgreSQL 12.0 (Debian 12.0-2.pgdg100+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 8.3.0-6) 8.3.0, 64-bit
db_1           | 2019-11-09 21:57:25.039 UTC [1] LOG:  listening on IPv4 address "0.0.0.0", port 5432
db_1           | 2019-11-09 21:57:25.039 UTC [1] LOG:  listening on IPv6 address "::", port 5432
db_1           | 2019-11-09 21:57:25.052 UTC [1] LOG:  listening on Unix socket "/var/run/postgresql/.s.PGSQL.5432"
db_1           | 2019-11-09 21:57:25.071 UTC [59] LOG:  database system was shut down at 2019-11-09 21:57:24 UTC
db_1           | 2019-11-09 21:57:25.077 UTC [1] LOG:  database system is ready to accept connections
myapp-tests_1  | Creating tables ...
myapp-tests_1  | Creating table 'users'
myapp-tests_1  | Tables created succesfully
myapp-tests_1  | yarn run v1.19.0
myapp-tests_1  | $ mocha --timeout 10000 --bail
myapp-tests_1  | 
myapp-tests_1  | 
myapp-tests_1  |   Users
myapp-tests_1  | Mock server started on port: 8002
myapp-tests_1  |     ✓ should create a new user (151ms)
myapp-tests_1  |     ✓ should get the created user
myapp-tests_1  |     ✓ should not create user if mail is spammy
myapp-tests_1  |     ✓ should not create user if spammy mail API is down
myapp-tests_1  | 
myapp-tests_1  | 
myapp-tests_1  |   4 passing (234ms)
myapp-tests_1  | 
myapp-tests_1  | Done in 0.88s.
myapp-tests_1  | 2019/11/09 21:57:26 Command finished successfully.
tuto-api-e2e-testing_myapp-tests_1 exited with code 0

We can see that db is the container that initializes the longest. Makes sense. Once its done the tests start.

The total runtime on my laptop is 16 seconds. Compared to the 880ms used to actually execute the tests it is a lot. In practice tests that run under 1 minute are gold as it is almost immediate feedback. The 15'ish seconds overhead are a buy in time that will be constant as you add more tests. You could add hundreds of tests and still keep execution time under 1 minute.

Voila! We have our test framework up and running. In a real world project the next steps would be to enhance functional coverage of your API with more tests. Let's consider CRUD operations covered. It's time to add more elsements to our test environment.

Adding a Redis cluster

Let's add another element to our API environment to understand what it takes. Spoiler alert: it's not much.

Let us imagine that our API keeps user sessions in a Redis cluster. If you wonder why we would do that, imagine 100 instances of your API in production. Users hit one or another server based on round robin load balancing. Every request needs to be authenticated. It requires user profile data to check for privileges and other application specific business logic. One way to go is to make a round trip to the database to fetch the data every time you need it, but that is not very efficient. Using an in memory database cluster makes the data available across all servers for the cost of a local variable read.

This is how you enhance your Docker compose test environment with an additional service.

Let’s add a Redis cluster from the official Docker image (I've only kept the new parts of the file):

services:
  db:
    ...

  redis:
    image: "redis:alpine"
    expose:
      - 6379

  myapp:
    environment:
      APP_REDIS_HOST: redis
      APP_REDIS_PORT: 6379
    ...
  myapp-tests:
    command: dockerize ... -wait tcp://redis:6379 ...
    environment:
      APP_REDIS_HOST: redis
      APP_REDIS_PORT: 6379
      ...
    ...

You can see it's not much. We added a new container called redis. It uses the official minimal redis image called

redis:alpine

. We added Redis host and port configuration to our API container. And we've made tests wait for it as well as the other containers before executing the tests.

Let’s modify our application to actually use the Redis cluster:

const redis = require('redis').createClient({
  host: config.redis.host,
  port: config.redis.port,
})

...

app.route('/api/users').post(async (req, res, next) => {
  try {
    const { email, firstname } = req.body;
    // ... validate inputs here ...
    const userData = { email, firstname };
    const result = await db('users').returning('id').insert(userData);
    const id = result[0];
    
    // Once the user is created store the data in the Redis cluster
    await redis.set(id, JSON.stringify(userData));
    
    res.status(201).send({ id, ...userData });
  } catch (err) {
    console.log(`Error: Unable to create user: ${err.message}. ${err.stack}`);
    return next(err);
  }
});

Let's now change our tests to check that the Redis cluster is populated with the right data. That's why the myapp-tests container also gets the Redis host and port configuration in

docker-compose.yml

it("should create a new user", done => {
  chai
    .request(SERVER_URL)
    .post("/api/users")
    .send(TEST_USER)
    .end((err, res) => {
      if (err) throw err;
      res.should.have.status(201);
      res.should.be.json;
      res.body.should.be.a("object");
      res.body.should.have.property("id");
      res.body.should.have.property("email");
      res.body.should.have.property("firstname");
      res.body.id.should.not.be.null;
      res.body.email.should.equal(TEST_USER.email);
      res.body.firstname.should.equal(TEST_USER.firstname);
      createdUserId = res.body.id;

      redis.get(createdUserId, (err, cacheData) => {
        if (err) throw err;
        cacheData = JSON.parse(cacheData);
        cacheData.should.have.property("email");
        cacheData.should.have.property("firstname");
        cacheData.email.should.equal(TEST_USER.email);
        cacheData.firstname.should.equal(TEST_USER.firstname);
        done();
      });
    });
});

See how easy this was. You can build a complex environment for your tests like you assemble Lego bricks.

We can see another benefit of this kind of containerized full environment testing. The tests can actually look into the environments components. Our tests can not only check that our API returns the proper response codes and data. We can check that data in the Redis cluster have the proper values. We could also check the database content.

Adding API mocks

A common element for API components is to call other API components.

Let's say our API needs to check for spammy user emails when creating a user. The check is done using a third party service:

const validateUserEmail = async (email) => {
  const res = await fetch(`${config.app.externalUrl}/validate?email=${email}`);
  if(res.status !== 200) return false;
  const json = await res.json();
  return json.result === 'valid';
}

app.route('/api/users').post(async (req, res, next) => {
  try {
    const { email, firstname } = req.body;
    // ... validate inputs here ...
    const userData = { email, firstname };

    // We don't just create any user. Spammy emails should be rejected
    const isValidUser = await validateUserEmail(email);
    if(!isValidUser) {
      return res.sendStatus(403);
    }

    const result = await db('users').returning('id').insert(userData);
    const id = result[0];
    await redis.set(id, JSON.stringify(userData));
    res.status(201).send({ id, ...userData });
  } catch (err) {
    console.log(`Error: Unable to create user: ${err.message}. ${err.stack}`);
    return next(err);
  }
});

Now we have a problem for testing anything. We can't create any users if the API to detect spammy emails is not available . Modifying our API to bypass this step in test mode is a dangerous cluttering of the code.

Even if we could use the real third party service, we don't want to do that. As a general rule our tests should not depend on external infrastructure. First of all, because you will probably run your tests a lot as part of your CI process. It’s not that cool to consume another production API for this purpose. Second of all the API might be temporarily down, failing your tests for the wrong reasons.

The right solution is to mock the external APIs in our tests.

No need for any fancy framework. We'll build a generic mock in vanilla JS in ~20 lines of code. This will give us the opportunity to control what the API will return to our component. It allows to test error scenarios.

Now let’s enhance our tests.

const express = require("express");

...

const MOCK_SERVER_PORT = process.env.MOCK_SERVER_PORT || 8002;

// Some object to encapsulate attributes of our mock server
// The mock stores all requests it receives in the `requests` property.
const mock = {
  app: express(),
  server: null,
  requests: [],
  status: 404,
  responseBody: {}
};

// Define which response code and content the mock will be sending
const setupMock = (status, body) => {
  mock.status = status;
  mock.responseBody = body;
};

// Start the mock server
const initMock = async () => {
  mock.app.use(bodyParser.urlencoded({ extended: false }));
  mock.app.use(bodyParser.json());
  mock.app.use(cors());
  mock.app.get("*", (req, res) => {
    mock.requests.push(req);
    res.status(mock.status).send(mock.responseBody);
  });

  mock.server = await mock.app.listen(MOCK_SERVER_PORT);
  console.log(`Mock server started on port: ${MOCK_SERVER_PORT}`);
};

// Destroy the mock server
const teardownMock = () => {
  if (mock.server) {
    mock.server.close();
    delete mock.server;
  }
};

describe("Users", () => {
  // Our mock is started before any test starts ...
  before(async () => await initMock());

  // ... killed after all the tests are executed ...
  after(() => {
    redis.quit();
    teardownMock();
  });

  // ... and we reset the recorded requests between each test
  beforeEach(() => (mock.requests = []));

  it("should create a new user", done => {
    // The mock will tell us the email is valid in this test
    setupMock(200, { result: "valid" });

    chai
      .request(SERVER_URL)
      .post("/api/users")
      .send(TEST_USER)
      .end((err, res) => {
        // ... check response and redis as before
        createdUserId = res.body.id;

        // Verify that the API called the mocked service with the right parameters
        mock.requests.length.should.equal(1);
        mock.requests[0].path.should.equal("/api/validate");
        mock.requests[0].query.should.have.property("email");
        mock.requests[0].query.email.should.equal(TEST_USER.email);
        done();
      });
  });
});

The tests now checks that the external API has been hit with the proper data during the call to our API.

We can also add other tests checking how our API behaves based on the external API response codes:

describe("Users", () => {
  it("should not create user if mail is spammy", done => {
    // The mock will tell us the email is NOT valid in this test ...
    setupMock(200, { result: "invalid" });

    chai
      .request(SERVER_URL)
      .post("/api/users")
      .send(TEST_USER)
      .end((err, res) => {
        // ... so the API should fail to create the user
        // We could test that the DB and Redis are empty here
        res.should.have.status(403);
        done();
      });
  });

  it("should not create user if spammy mail API is down", done => {
    // The mock will tell us the email checking service
    //  is down for this test ...
    setupMock(500, {});

    chai
      .request(SERVER_URL)
      .post("/api/users")
      .send(TEST_USER)
      .end((err, res) => {
        // ... in that case also a user should not be created
        res.should.have.status(403);
        done();
      });
  });
});

How you handle errors from third party APIs in your application is of course up to you. But you get the point.

To run these tests we need to tell the container myapp what is the base URL of the third party service:

  myapp:
    environment:
      APP_EXTERNAL_URL: http://myapp-tests:8002/api
    ...

  myapp-tests:
    environment:
      MOCK_SERVER_PORT: 8002
    ...

Conclusion and a few other thoughts

Hopefully this article gave you a taste of what Docker compose can do for you when it comes to API testing. The full example is here on GitHub.

Using Docker compose makes tests run fast in an environment close to production. It requires no adaptations to your component code. The only requirement is to support environment variables driven configuration.

The component logic in this example is very simple but the principles apply to any API. Your tests will just be longer or more complex. They also apply to any tech stack that can be put inside a container (that's all of them). And once you are there you are one step away from deploying your containers to production if need be.

If you have no tests right now this is how I recommend you should start. End to end testing with Docker compose. It is so simple you could have a first test running in a few hours. Feel free to reach out to me if you have questions or need advice. I'd be happy to help.

I hope you enjoyed this article and will start testing your APIs with Docker Compose. Once you have the tests ready you can run them out of the box on our continuous integration platform Fire CI.

One last idea to succeed with automated testing.

When it comes to maintaining large test suites, the most important feature is that tests are easy to read and understand. This is key to motivate your team to keep the tests up to date. Complex tests frameworks are unlikely to be properly used in the long run. Regardless of the stack for your API, you might want to consider using chai/mocha to write tests for it. It might seem unusual to have different stacks for runtime code and test code, but if it gets the job done ... As you can see from the examples in this article, testing a REST API with chai/mocha is as simple as it gets. The learning curve is close to zero. So if you have no tests at all and have a REST API to test written in Java, Python, RoR, .NET or whatever other stack, you might consider giving chai/mocha a try.

If you wonder how to get start with continuous integration at all, I have written a broader guide about it. Here it is: How to get started with Continuous Integration

Originally published on the Fire CI Blog.

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