How to write a unit test

See also: Unit testing

This document demonstrates how to write a unit test for Juju.


Prepare for the test

Create package_test.go

This step is necessary only if this file doesn’t already exist.

Each package requires a package_test.go file if we wish any of our tests to run.

Below is a standard package_test.go file for an example package called magic. We import the “testing” package from the standard library and then the gocheck package as gc. We also create a function Test that will be the entry-point into our test suites.

// Copyright 20XX Canonical Ltd.
// Licensed under the AGPLv3, see LICENCE file for details.

package magic_test

import (

    gc ""

func Test(t *testing.T) {

You will sometimes see package_test.go files which use testing.MgoTestPackage as their entrypoint. This is required to run old-style JujuConnSuite tests, which test against a running instance of MongoDB.

These tests are deprecated and are actively being removed. No more should be added.

Create <code-filename>_test.go

In the code directory, for each file that you want to test (say, a source code file called magic1.go), create a <code-filename>_test.go (e.g. magic1_test.go).

Import gocheck

See also: gocheck

In magic1_test.go, import the gocheck package as gc:

import (
    gc ""

gc is the usual alias for gocheck across all the Juju repositories.

Add a unit test suite

See also: Unit test suite

Also in magic1_test.go, add a unit test suite.

See more: How to create a unit test suite

Once the test suite structure has been created, it needs to be registered with gc or the tests will not run. You can do by passing a pointer to an instance of our suite to the gc.Suite function.

type magicSuite struct{}

var _ = gc.Suite(&magicSuite{})

Write the test

See also: Checkers

In magic1_test.go, below the test suite, start adding your unit test functions.

The process is as follows: You target some behavior (usually a function) in the code file (in our case, magic1). You then write a test for it, where the test usually follows the same Given, When, Then logic.

For example, suppose your magic1.go file defines a simple function called Sum:

func Sum(a, b int) int {
	return a + b

Then, in your magic1_test.go file you can write a test for it as follows (where gc.Equals is a Checker):

// GIVEN a equals 5 AND b equals 3
// WHEN a and b are summed 
// THEN we get 8
func (s *magicSuite) TestSum(c *gc.C) {
	a := 5
	b := 3

	res := magic.Sum(a,b)

	c.Assert(res, gc.Equals, 8)

Run the test

Finally, to run the test, do:

go test

This will run all the tests registered in the magic package, including the one we just wrote.

You can also chose to run specific tests or suites, using the -check.f flag for gocheck

go test -check.f magicSuite         # run the magicSuite only
go test -check.f magicSuite.TestSum # run the test TestSum in magicSuite only

Contributors: @jack-shaw

Last updated 4 months ago. Help improve this document in the forum.