add mocha assertions tutorial

Author: vkarpov15

src/tutorials.js

@@ -5,6 +5,14 @@ const moment = require('moment');
 const axiosPath = require('./axiosPath');
 
 const tutorials = [
+  {
+    title: 'Assertions in Mocha',
+    raw: './tutorials/mocha/assertions.md',
+    url: '/tutorials/mocha/assertions',
+    description: 'Mocha doesn\'t have a built-in assertion library, but here are a few options.',
+    tags: ['mocha'],
+    date: moment('2023-08-09')
+  },
   {
     title: 'Using `it.skip()` in Mocha',
     raw: './tutorials/mocha/it-skip.md',

tutorials/mocha/assertions.md

@@ -0,0 +1,62 @@
+One of the most common criticisms of Mocha is that it doesn't include any assertion tools.
+It is impossible to write meaningful tests without some sort of assertions.
+The idea is that [Node's built-in `assert` module](/tutorials/node/assert) is good enough for most use cases.
+
+```javascript
+const assert = require('assert');
+
+describe('add', function() {
+  it('adds two numbers', function() {
+    assert.equal(add(1, 2), 3);
+  });
+
+  it('concatenates strings', function() {
+    assert.equal(add('hello ', 'world'), 'hello world');
+  });
+});
+
+function add(a, b) {
+  return a + b;
+}
+```
+
+We recommend using Node's built-in `assert` module with Mocha tests by default.
+`assert.ok()`, `assert.equal()`, `assert.strictEqual()`, `assert.throws()`, `assert.rejects()`, and `assert.deepStrictEqual()` cover every assertion we've wanted to write over the last several years.
+
+Alternative Approach: Chai
+----------
+
+[Chai](/tutorials/mocha/chai) is an assertion library that is commonly used with Mocha.
+Chai exports several different flavors of assertions.
+The [`expect`](https://www.chaijs.com/api/bdd/) flavor is the most common.
+
+```javascript
+const { expect } = require('chai');
+
+describe('sum()', function() {
+  it('adds two numbers', function() {
+    // `expect()` takes in a parameter value and returns what Chai calls
+    // a "chain"
+    expect(add(2, 4)).to.equal(6);
+  });
+
+  it('ignores additional arguments', function() {
+    expect(add(2, 4, 6)).to.equal(6);
+  });
+});
+
+function add(a, b) {
+  return a + b;
+}
+```
+
+Chai's assertions are popular because they read more like English.
+You can write expectations like the following:
+
+```javascript
+expect([1, 2]).to.be.an('array').that.does.not.include(3);
+```
+
+This syntax can be neat, especially for non-technical readers.
+However, Chai syntax is fairly verbose, and can be difficult to write without practice.
+We recommend using `assert` because `assert`'s API is simpler: you can get by with just 6 functions.