Unit testing JavaScript with JsUnit


function capitalize(str) {
  return str?

This is my JavaScript function for capitalizing the first letter of a String. I was sure that I got capitalization right, but I wasn’t too sure about how this function would handle null/empty values.

So I wrote a unit test, for JsUnit:


<script language="javascript" src="jsUnitCore.js"></script>
<script language="javascript" src="my-script.js"></script>
<script language="javascript">

function testCapitalize() {
  assertEquals("Foo bar", capitalize("foo bar"));
  assertEquals("Foobar", capitalize("foobar"));
  assertEquals("F", capitalize("f"));
  assertEquals("", capitalize(""));


The test requires loading the jsUnitCore.js script. This test loads a local copy but you could use the online version as well. Then I can run the test with my local TestRunner.

Status: Done (0.156 seconds)
Runs: 1   Errors: 0   Failures: 0

Now I know that my function is correct!

When a test fails the assertion error looks like this:

1. my-script.test.html:testCapitalize failed

Expected <Foobar> (String) but was <foobar> (String)

Stack trace follows:
> JsUnitException
> _assert
> assertEquals
> testCapitalize

Happy testing!

One Response to “Unit testing JavaScript with JsUnit”

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