Adding tests

Last updated on 2025-09-30 | Edit this page

Overview

Questions

  • What are unit tests?
  • How are tests organized in Julia?

Objectives

  • Learn to create unit tests and test sets using the Test standard library

Unit tests

Now that Melissa has released her first package she fears that future changes will impact the existing functionality of her package. This can be prevented by adding tests to her package.

Looking at the structure of other packages Melissa figured out that tests usually go in a separate test folder next to the src folder. This should contain a runtests.jl file.

The standard library Test provides the functionality for writing tests: namely, the macros @test and @testset.

@test can be used to test a single equality, such as

JULIA 

using Test
@test 1 + 1 == 2

OUTPUT 

Test Passed

Several tests can be grouped in a test set with a descriptive name

JULIA 

using Test
@testset "Test arithmetic equalities" begin
    @test 1 + 1 == 2
end

OUTPUT 

Test.DefaultTestSet("Test arithmetic equalities", Any[], 1, false, false, true, 1.731669987513481e9, 1.731669987543832e9, false)

Melissa sees that she can run her package tests using the pkg mode of the REPL:

JULIA 

(MelissasModule) pkg> test

ERROR 

ERROR: Package MelissasModule did not provide a `test/runtests.jl` file

Remember from earlier that the conventional project structure included a test/runtests.jl file? This file is the entry point for package tests.

Test environment

Melissa needed to add Test to her package in order to run the code above, but actually Test is not needed for her package other than testing. Melissa needs to generate a testing environment with its own dependencies:

JULIA 

(MelissasModule) pkg> activate projects/MelissasModule/test

OUTPUT 

  Activating new project at `~/projects/MelissasModule/test`

JULIA 

(test) pkg> add Test

OUTPUT 

  Resolving package versions...
    Updating `~/projects/MelissasModule/test/Project.toml`
  [8dfed614] + Test v1.11.0
    Updating `~/projects/MelissasModule/test/Manifest.toml`
  [2a0f44e3] + Base64 v1.11.0
  [b77e0a4c] + InteractiveUtils v1.11.0
  [56ddb016] + Logging v1.11.0
  [d6f4376e] + Markdown v1.11.0
  [9a3f8284] + Random v1.11.0
  [ea8e919c] + SHA v0.7.0
  [9e88b42a] + Serialization v1.11.0
  [8dfed614] + Test v1.11.0

Now Melissas project structure looks like this:

MelissasModule/
├── Project.toml
├── src
│   └── MelissasModule.jl
└── test
    └── Project.toml

And the test/Project.toml has:

[deps]
Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
Callout

Using just one Project.toml

Alternatively, Melissa could include the Test package as an “extra” in her top-level Project.toml and require that dependency for the test target.

Check out the Project.toml from the Example.jl project for an example of this.

Challenge

Challenge

Create a test for MelissasModule in test/runtests.jl

Create a test that ensures that shoot_distance returns a value that is between target - ε and target + ε.

JULIA 

using MelissasModule
using Test

@testset "Test hitting target" begin
    imprecise_trebuchet = Trebuchet(500.0, 0.25pi)
    environment = Environment(5, 100)
    precise_trebuchet = aim(imprecise_trebuchet, environment)
    final_distance = shoot_distance(precise_trebuchet, environment)
    @test 100 - 0.1 <= final_distance <= 100 + 0.1
    # default ε is 0.1
    # could also use:
    # @test abs(final_distance - 100) <= 0.1
end

Now Melissa can run this test from pkg mode:

JULIA 

(MelissasModule) pkg> test

OUTPUT 

     Testing MelissasModule
      Status `/tmp/jl_TTQJwg/Project.toml`
  [34b7a6fa] MelissasModule v0.1.0 `~/projects/MelissasModule`
  [8dfed614] Test v1.11.0
      Status `/tmp/jl_TTQJwg/Manifest.toml`
  [...]
  ⋮
  # Skipping output here setting up the temporary testing environment
  ⋮
     Testing Running tests...
Test Summary:       | Pass  Total   Time
Test hitting target |    1      1  19.7s
     Testing MelissasModule tests passed
Key Points
  • Tests are important