Unit testing JavaScript using Mocha and Node

Unit testing
JavaScript
using Mocha and Node.js

Josh Mock
Senior JavaScript architect at Emma
Twitter:
Email:
@JoshMock
josh@joshmock.com

What is unit testing?
Write code to test code
Ensures code works as expected
Granular, single-focus assertions
Not a substitute for QA

Why unit test?
Confidence
Easier refactoring
Less regression
Less complexity
TDD is fun!

Install Node.js
node.js.org/download/
OS X (with Homebrew installed):
brew install node

Install Mocha
npm install -g mocha

Test some code!
var Car = function () {
this.make = "Honda";
this.model = "Civic";
};

Run, tests, run
mocha path/to/test/file.js

How to write good tests
Test results, not internals
One focus per test
Testing DOM changes is bold

Simple, single-purpose functions
// bad
var numbers = {
list: [1, 2, 3],
add: function (newNum) {
this.list.push(newNum);
this.list.sort();
}
};
// good
var numbers = {
list: [1, 2, 3],
},
sort: function () {
this.list.sort();
}
};

Avoid tight coupling of components
var numbers = {
list: [1, 2, 3],
}
};
// bad
var math = {
add: function () {
var total = 0;
for (var i = 0; i < numbers.list.length; i++) {
total += numbers.list[i];
}
return total;
},
average: function () {
return this.add() / numbers.list.length;
}
};
alert(math.average());
// good
var math = {
add: function (numList) {
var total = 0;
for (var i = 0; i < numList.length; i++) {
total += numList[i];
}
return total;

Separate business logic from UI
(and avoid anonymous functions/callbacks)
var numbers = [2, 4, 1, 3, 5];
// bad
$("a.sort-numbers").on("click", function (e) {
e.preventDefault();
numbers.sort();
});
// good
var sortNumbers = function (e) {
e && e.preventDefault && e.preventDefault();
numbers.sort();
};
$("a.sort-numbers").on("click", sortNumbers);

var asyncSort = function (numbers, callback) {
setTimeout(function () {
callback(numbers.sort());
}, 10);
};

define("asyncSort", function () {
it("should sort my numbers", function (done) {
asyncSort([1, 3, 2], function (result) {
assert.deepEqual(result, [1, 2, 3]);
done();
});
});
});

Spies
var sinon = require("sinon");
it("runs jQuery.ajax", function () {
sinon.spy($, "ajax");
doAjaxCall();
assert($.ajax.calledOnce);
$.ajax.restore();
});
it("does some thing that takes forever", function () {
someGlobal.slowFunction = sinon.spy();
callSlowFunction();
assert.equal(someGlobal.slowFunction.callCount, 1);
assert(someGlobal.slowFunction.calledWith(1, "two", 3));
});

Stubs
it("returns the age of a person with data stored in the database", function () {
Database.get = sinon.stub().returns({
name: "Joe",
age: 33
});
var getAge = function () {
return Database.get("Joe").age;
};
assert.equals(getAge(), 33);
});

Mocks
it("should get the desired car from the database", function () {
var mock = sinon.mock(Database);
mock
.expects("getCar")
.withExactArgs("Honda Civic")
.once()
var car = new Car();
car.get("Honda Civic");
assert(mock.verify());
});

Fake timers
it("should save after 30 seconds", function () {
var clock = sinon.useFakeTimers();
sinon.spy($, "ajax");
delayedSave();
clock.tick(30001);
assert($.fn.ajax.called);
$.ajax.restore();
});

jsdom and node-jquery
Test browser-dependent code
Make Node think it's a browser
Test jQuery DOM manipulations
Go through all stages of grief getting it to work
Ponder using a browser-based framework instead

Install
npm install -g jsdom && npm install -g jquery

Set up
GLOBAL.document = require("jsdom").jsdom();
GLOBAL.window = document.createWindow();
GLOBAL.$ = GLOBAL.jQuery = require("jquery").create(window);

Use
it("should change div background color to blue", function () {
$("body").html('<div id="mydiv"></div>');
$("#mydiv").css("background", "blue");
assert.equal($("#mydiv").css("background"), "blue");
});

No headless browser
No GUI running in background
No guarantees

THE END
Questions?
Twitter:
Email:
@JoshMock
josh@joshmock.com
github.com/JoshMock/mocha-node-slides

Unit testing JavaScript using Mocha and Node

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