mocha-slonik v9.0.0

mocha-slonik

Slonik transaction support for Mocha test framework.

Table of Contents

• Why does mocha-slonik exist?
  • Slonik’s createMockPool vs mocha-slonik
• How it works
• Version compatibility
• Installation
• Usage
  • Without Mocha Root Hook plugin
  • With Mocha Root Hook plugin
• API
  • rollback
  • currentTransaction
• Best practices
  • Always rollback transaction in after/afterEach block
  • Use global Root Hook to DRY up boilerplating
• Developing
• Running tests
• Limitations
  • Lack of copyFromBinary support

Why does mocha-slonik exist?

This package exists as a way for developers to run integration tests against a real database without having to worry about cleaning up the test data after each test. Since each test cases are wrapped in its own transaction that is automatically rolled back, you can ensure that your tests are isolated from each other: an earlier test that affects a row does not affect subsequent tests that may depend on the same row.

Slonik’s createMockPool vs mocha-slonik

Slonik already provides a way to mock queries against the database by using a combination of createMockPool and createMockQueryResult. This is usually sufficient for lightweight unit testing individual functions that calls Slonik query methods and is great for running tests that does not need a running instance of PostgreSQL.

See: Mocking Slonik

How it works

mocha-slonik is a Root Hook Plugin for Mocha that utilizes ts-mock-imports to return a stubbed bindPool function that wrap most of the Slonik query methods in a transaction that automatically rolls back after each test.

Version compatibility

mocha-slonik follows Semantic Versioning specification. Each major version breaks backwards compatibility with Slonik and Mocha versions.

Refer to the compatibility chart below for picking the mocha-slonik version that works with Slonik and Mocha versions in your project.

Installation

Install this library as a dev dependency in your project:

npm i -D mocha-slonik

Usage

Without Mocha Root Hook plugin

This is recommended for applications that utilize factory design pattern and does not wish to introduce global side effect on the Slonik module itself.

This is especially useful if you want fine control over when you want to rollback the transactions. For example, if you have a nested describe block but only wish to rollback on the inner block, you can choose to rollback in the inner after function.

import { createPool } from "mocha-slonik";

describe("outer block", function () {
  let pool;

  before(function () {
    pool = createPool(/* ... */);
  });

  describe("test group 1", function () {
    // Group 1 rolls back after the entire group has completed running.
    after(async function () {
      await pool.rollback();
    });

    it("should insert data", async function () {
      // ...
    });

    it("should test something else with inserted data", async function () {
      // ...
    });
  });

  describe("test group 2", function () {
    // Group 2 rolls back after EACH test completed running.
    afterEach(async function () {
      await pool.rollback();
    });

    it("shouldn't be affected by changes to data by tests in group 1", async function () {
      // ...
    })
  });

});

This ensures the tests that are grouped by the inner describe block see the side effects of previous tests within the group but isolated from other tests outside of the inner describe block.

Example Express.js project

createServer.ts

export const createServer = ({ app, pool }, listenPort) => {
  app.use(json);
  app.post("/articles", async (req, res, next) => {
    const { title, body } = req.body;
    const newArticle = await pool.query(sql`
      INSERT INTO articles (title, body) VALUES (${title}, ${body}) RETURNING *;
    `);

    res.status(201).json(newArticle);
  });

  app.get("/articles/:articleId", async (req, res, next) => {
    const article = await pool.one(sql`
      SELECT * FROM articles WHERE id = ${req.params.articleId} LIMIT 1;
    `);

    res.json(article);
  });

  return app.listen(listenPort ?? 8080);
}

server.ts

import express, { json } from "express";
import { createPool, sql } from "slonik";
import { createServer } from "app";

const pool = createPool(process.env.DATABASE_URL);
export const app = express();
export const server = createServer({ app, pool });

server.spec.ts

import { expect, use } from "chai";
import chaiHttp from "chai-http";
import { createPool } from "mocha-slonik";
import { sql } from "slonik";
import { createServer } from "./app";

use(chaiHttp);

describe("/articles", function () {
  let app;
  let client;
  let server;
  let pool;

  before(async function () {
    app = express();
    pool = createPool(process.env.DATABASE_URL);
    server = createServer({ app, createPool });
    client = chai.request(server).keepOpen();
  });

  beforeEach(async function () {
    // Assume 3 items of test fixture data to be inserted into the database.
    const testFixtures = [
      [ /* ... */ ],
      // ...
    ];

    // Bulk insert test fixture
    await pool.query(sql`
      INSERT INTO articles (title, body)
      SELECT * FROM ${sql.unnest(testFixtures, ["text", "text"])};
    `);
  });

  // Remember to rollback the pool afterEach test.
  afterEach(async function () {
    await pool.rollback();
  });

  after(function (done) {
    pool.end().then(() => {
      client.close();
      server.close(done);
    });
  });

  it("should insert a new article", async function () {
    const payload = {
      title: "Never Gonna Give You Up",
      body: "We're no strangers to love"
    };

    // oldCount should be 3 based on test fixture.
    const oldCount = await pool.oneFirst(sql`SELECT COUNT(*) FROM articles;`);

    const response = await client.post("/articles").send(payload);

    // newCount should now be 4
    const newCount = await pool.oneFirst(sql`SELECT COUNT(*) FROM articles;`);

    expect(response.body).to.eql(payload);
    expect(newCount).to.be.above(oldCount);
  });

  it("should get an article by id", async function () {
    const response = await client.get("/articles/1").send();
    const expected = {
      title: "Lorem ipsum",
      body: "Lorem ipsum dolor amit"
    };

    // Previous test shouldn't affect this test and count return 3
    const count = await pool.oneFirst(sql`SELECT COUNT(*) FROM articles;`);

    expect(response.body).to.eql(expected);
  });
});

With Mocha Root Hook plugin

This usage pattern is recommended for applications that cannot utilize factory design pattern.

Require mocha-slonik/register in Mocha CLI:

mocha --require mocha-slonik/register tests/**/*.ts

Or update .mocharc configuration file:

{
  "require": [
    "mocha-slonik/register"
  ]
}

That's it! All of your Slonik queries will be wrapped in a transaction in both your application code and your tests that will automatically be rolled back after each test block.

Example Express.js project

app.ts

import express, { json } from "express";
import { createPool, sql } from "slonik";

const pool = createPool(process.env.DATABASE_URL);
export const app = express();

app.use(json);
app.post("/articles", async (req, res, next) => {
  const { title, body } = req.body;
  const newArticle = await pool.query(sql`
    INSERT INTO articles (title, body) VALUES (${title}, ${body}) RETURNING *;
  `);

  res.status(201).json(newArticle);
});

app.get("/articles/:articleId", async (req, res, next) => {
  const article = await pool.one(sql`
    SELECT * FROM articles WHERE id = ${req.params.articleId} LIMIT 1;
  `);

  res.json(article);
});

app.listen(8080);

app.spec.ts

import { expect, use } from "chai";
import chaiHttp from "chai-http";
import { createPool, sql } from "slonik";
import { app } from "./app";

use(chaiHttp);

describe("/articles", function () {
  let client;
  let server;
  let pool;

  before(async function () {
    server = app.listen(9090);
    client = chai.request(server).keepOpen();
    pool = createPool(process.env.DATABASE_URL);
  });

  beforeEach(async function () {
    // Assume 3 items of test fixture data to be inserted into the database.
    const testFixtures = [
      [ /* ... */ ],
      // ...
    ];

    // Bulk insert test fixture (rolls back after each test)
    await pool.query(sql`
      INSERT INTO articles (title, body)
      SELECT * FROM ${sql.unnest(testFixtures, ["text", "text"])};
    `);
  });

  after(function (done) {
    pool.end().then(() => {
      client.close();
      server.close(done);
    });
  });

  it("should insert a new article", async function () {
    const payload = {
      title: "Never Gonna Give You Up",
      body: "We're no strangers to love"
    };

    // oldCount should be 3 based on test fixture.
    const oldCount = await pool.oneFirst(sql`SELECT COUNT(*) FROM articles;`);

    const response = await client.post("/articles").send(payload);

    // newCount should now be 4
    const newCount = await pool.oneFirst(sql`SELECT COUNT(*) FROM articles;`);

    expect(response.body).to.eql(payload);
    expect(newCount).to.be.above(oldCount);
  });

  it("should get an article by id", async function () {
    const response = await client.get("/articles/1").send();
    const expected = {
      title: "Lorem ipsum",
      body: "Lorem ipsum dolor amit"
    };

    // Previous test shouldn't affect this test and count return 3
    const count = await pool.oneFirst(sql`SELECT COUNT(*) FROM articles;`);

    expect(response.body).to.eql(expected);
  });
});

API

The query methods exposed by mocha-slonik is nearly identical to query methods exposed by default Slonik pool instance except for few additional methods, properties and limitations.

rollback

rollback method is used to rollback the global transaction in mocha-slonik. It should only be used in after or afterEach blocks in your tests. Usage anywhere else is considered anti-pattern and may introduce side effects that are hard to debug.

Example:

import { createPool } from "mocha-slonik";

describe("/articles", function () {
  let pool;

  before(async function () {
    pool = createPool(process.env.DATABASE_URL);
  });

  // ...

  // Remember to rollback the pool afterEach test.
  afterEach(async function () {
    await pool.rollback();
  });

  // ...
});

currentTransaction

currentTransaction getter is a property that returns the current transaction if one has been started, undefined otherwise.

Best practices

Always rollback transaction in after/afterEach block

Unless you are using the Mocha Root Hook plugin, you should always rollback your transactions in after or afterEach block instead of individual it test cases. This prevents unexpected surprises if your test code throws errors or has rejected promises because after/afterEach is guaranteed to run even if your tests fail or contains errors.

Do:

import { createPool } from "mocha-slonik";

describe("Rollback on afterEach", function () {
  let pool;

  before(async function () {
    pool = createPool(process.env.DATABASE_URL);
  });

  // ...

  // Rollback the transaction after each test.
  afterEach(async function () {
    await pool.rollback();
  });

  // ...
});

describe("Rollback on after", function () {
  let pool;

  before(async function () {
    pool = createPool(process.env.DATABASE_URL);
  });

  // ...

  // Rollback the transaction after the entire group of tests in the describe block.
  after(async function () {
    await pool.rollback();
  });

  // ...
});

Don’t:

import { expect } from "chai";
import { createPool } from "mocha-slonik";
import { sql } from "slonik";

describe("Rollback on individual test cases", function () {
  let pool;

  before(async function () {
    pool = createPool(process.env.DATABASE_URL);
  });

  it("Bad example 1", async function () {
    const result = await pool.oneFirst(sql`SELECT 1`);
    expect(result).to.eq(0);

    // If the assertion above fails, the rollback won't execute.
    await pool.rollback();
  });

  it("Bad example 2", async function () {
    const result = await pool.oneFirst(sql`SELECT 1`);

    // Simulate some thrown error in the test code
    await Promise.reject(new Error());

    // The rollback won't excute even if the rollback is above the assertion this time.
    await pool.rollback();

    expect(result).to.eql(1);
  });

  it("Bad example 3", async function () {
    try {
      const result = await pool.oneFirst(sql`SELECT 1`);

      // Simulate some thrown error in the test code
      await Promise.reject(new Error());

      expect(result).to.eql(1);
    } catch (error) {
      throw error;
    } finally {
      // Technically works but you have to remember to add the try/finally block for EVERY test case.
      await pool.rollback();
    }
  });
});

Use global Root Hook to DRY up boilerplating

If you’re not using the Root Hook plugin provided by this library but wish to DRY up your setup and teardown code across multiple test files, you should define a global Root Hook in your tests directory and require it.

tests/global.ts:

import { Server } from "http";
import express from "express";
import { RootHookObject } from "mocha";
import { DatabasePool, createPool } from "mocha-slonik";

// See example at: https://github.com/AndrewJo/mocha-slonik#createserverts
import { createServer } from "../src/server";

declare global {
  namespace Mocha {
    interface Context {
      pool: DatabasePool;
      server: Server;
    }
  }
}

export const mochaHooks: RootHookObject = {
  async beforeAll() {
    // The pool and HTTP server is now available for all of the tests through the context object.
    this.pool = await createPool("postgres://localhost:5432/testdb");
    this.server = createServer({ app: express(), pool: this.pool });
  }
};

.mocharc.yaml:

require:
  - "ts-node/register"
  - "tests/global"

Developing

Please read CONTRIBUTING.md before making changes to this project.

Running tests

To run tests:

npm run build && npm test

To run test with coverage:

npm run test:coverage && npx nyc reporter --reporter=lcov

This will generate an HTML coverage report at: ./coverage/lcov-report/index.html.

Limitations

This library overrides parts of Slonik that is not part of its public API and may break in the future. Please make sure to check the release notes for compatible Slonik versions before using this library.

Lack of copyFromBinary support

Due to the lack of support for transactions in copyFromBinary method and the potential for being deprecated in the future versions, calling copyFromBinary will immediately reject with an error message.

copyFromBinary support has been officially removed in Slonik starting from v34.0.0. This library no longer contains copyFromBinary function starting from v8.