Unit Testing

For lua modules, I would recommend the library TestEZ. It was developed in-house by Roblox engineers to allow for behavior driven tests. It allows you to specify a location where test files exist and will gives you pretty detailed output as to how your tests did.

This example will run in RobloxStudio, but you can pair it with other libraries like Lemur for command-line and continuous integration workflows. Anyways, follow these steps :

1. Get the TestEZ Library into Roblox Studio

1. Download Rojo. This program allows you to convert project directories into .rbxm (Roblox model object) files.
2. Download the TestEZ source code.
3. Open a Powershell or Terminal window and navigate into the downloaded TestEZ directory.
4. Build the TestEZ library with this command rojo build --output TestEZ.rbxm .
5. Make sure that it generated a new file called TestEZ.rbxm in that directory.
6. Open RobloxStudio to your place.
7. Drag the newly created TestEZ.rbxm file into the world. It will unpack the library into a ModuleScript with the same name.
8. Move this ModuleScript somewhere like ReplicatedStorage.

2. Create unit tests

A common way to structure code is with your code classes in ModuleScripts and their tests right next to them. So let's say you have a simple utility class in a ModuleScript called MathUtil

local MathUtil = {}

function MathUtil.add(a, b)
    assert(type(a) == "number")
    assert(type(b) == "number")
    return a + b
end

return MathUtil

To create tests for this file, create a ModuleScript next to it and call it MathUtil.spec. This naming convention is important, as it allows TestEZ to discover the tests.

return function()
    local MathUtil = require(script.parent.MathUtil)
    
    describe("add", function()
        it("should verify input", function()
            expect(function()
                local result = MathUtil.add("1", 2)
            end).to.throw()
        end)
        
        it("should properly add positive numbers", function()
            local result = MathUtil.add(1, 2)
            expect(result).to.equal(3)
        end)
        
        it("should properly add negative numbers", function()
            local result = MathUtil.add(-1, -2)
            expect(result).to.equal(-3)
        end)
    end)
end

For a full breakdown on writing tests with TestEZ, please take a look at the official documentation.

3. Create a test runner

In this step, we need to tell TestEZ where to find our tests. So create a Script in ServerScriptService with this :

local TestEZ = require(game.ReplicatedStorage.TestEZ)

-- add any other root directory folders here that might have tests 
local testLocations = {
    game.ServerStorage,
}
local reporter = TestEZ.TextReporter
--local reporter = TestEZ.TextReporterQuiet -- use this one if you only want to see failing tests
 
TestEZ.TestBootstrap:run(testLocations, reporter)

4. Run your tests

Test results:
[+] ServerStorage
   [+] MathUtil
      [+] add
         [+] should properly add negative numbers
         [+] should properly add positive numbers
         [+] should verify input
3 passed, 0 failed, 0 skipped - TextReporter:87

Automation Testing

Unfortunately, there does not exist a way to fully automate the testing of your game.

You can use TestService to create tests that automate the testing of some interactions, like a player touching a kill block or checking bullet paths from guns. But there isn't a publicly exposed way to start your game, record inputs, and validate the game state.

There's an internal service for this, and a non-scriptable service for mocking inputs but without overriding CoreScripts, it's really not possible at this moment in time.