Getting Started

The Jest Roblox API is similar to the API used by JavaScript Jest.

Jest Roblox requires roblox-cli to run from the command line.

Add the JestGlobals and Jest package to your dev_dependencies in your rotriever.toml.

rotriever.toml

[dev_dependencies]
Jest = "3.9.1"
JestGlobals = "3.9.1"

Run rotrieve install to install Jest Roblox.

Create a default.project.json to set up your project structure and include the Packages directory created by rotriever.

default.project.json

{
    "name": "YourProject",
    "tree": {
        "$className": "Folder",
        "Packages": {
            "$path": "Packages",
            "Project": {
                "$path": "src"
            }
        }
    }
}

Create a spec.lua to point the test runner to the correct directory with your tests. This is the entrypoint for Jest Roblox. For more information, see runCLI Options.

spec.lua

local Packages = script.Parent.YourProject.Packages
local runCLI = require(Packages.Dev.Jest).runCLI

local processServiceExists, ProcessService = pcall(function()
    return game:GetService("ProcessService")
end)

local status, result = runCLI(Packages.Project, {
    verbose = false,
    ci = false
}, { Packages.Project }):awaitStatus()

if status == "Rejected" then
    print(result)
end

if status == "Resolved" and result.results.numFailedTestSuites == 0 and result.results.numFailedTests == 0 then
    if processServiceExists then
        ProcessService:ExitAsync(0)
    end
end

if processServiceExists then
    ProcessService:ExitAsync(1)
end

return nil

Inside src, create a basic configuration file.

jest.config.lua

return {
    testMatch = { "**/*.spec" }
}

Let's get started by writing a test for a hypothetical function that adds two numbers. First, create a sum.lua under your src directory.

sum.lua

return function(a, b)
    return a + b
end

Then, create a __tests__ directory under your src directory and create a sum.spec.lua in it. This will contain our actual test:

sum.spec.lua

local Workspace = script.Parent.Parent
local Packages = Workspace.Parent

local JestGlobals = require(Packages.Dev.JestGlobals)
local it = JestGlobals.it
local expect = JestGlobals.expect

local sum = require(Workspace.sum)

it('adds 1 + 2 to equal 3', function()
    expect(sum(1, 2)).toBe(3)
end)

caution

Any functionality needed must be explicitly required from JestGlobals, see Globals.

Finally, run your project using roblox-cli to run the tests and your tests should pass!

roblox-cli run --load.model default.project.json --run spec.lua --fastFlags.overrides EnableLoadModule=true

You just successfully wrote your first test using Jest Roblox!

This test used expect and toBe to test that two values were exactly identical. To learn about other things that Jest Roblox can test, see Using Matchers.