Testing Roblox games

Make code testable first

• Keep game rules in pure ModuleScripts (inputs → outputs, no services, no yields): damage formulas, inventory operations, shop pricing, state machines, serialization, validation. These are trivially testable.
• Services take their dependencies as parameters (dependency injection) so tests can pass fakes instead of real DataStores, remotes, or Players.

--!strict
-- ReplicatedStorage/Shared/Inventory.luau — pure logic, no Roblox services.
export type Inventory = { [string]: number }

local Inventory = {}

function Inventory.add(inventory: Inventory, itemId: string, amount: number, maxStack: number): (boolean, string?)
	if amount <= 0 or amount ~= math.floor(amount) then
		return false, "invalid amount"
	end
	local current = inventory[itemId] or 0
	if current + amount > maxStack then
		return false, "stack full"
	end
	inventory[itemId] = current + amount
	return true, nil
end

return Inventory

--!strict
-- A service that receives its data store, so tests can inject an in-memory fake.
type Store = {
	GetAsync: (self: Store, key: string) -> any,
	SetAsync: (self: Store, key: string, value: any) -> (),
}

local function newCurrencyService(store: Store)
	local service = {}
	function service.award(userId: number, amount: number): number
		local key = `User_{userId}`
		local balance = (store:GetAsync(key) or 0) + amount
		store:SetAsync(key, balance)
		return balance
	end
	return service
end

-- In tests: a fake store backed by a table.
local fakeData: { [string]: any } = {}
local fakeStore: Store = {
	GetAsync = function(_self, key)
		return fakeData[key]
	end,
	SetAsync = function(_self, key, value)
		fakeData[key] = value
	end,
}
print(newCurrencyService(fakeStore).award(1, 50))

return newCurrencyService

Jest Lua (recommended framework)

Port of Jest (describe/it/expect, mocks, snapshots). TestEZ is legacy; Jest Lua 3 includes a migration guide.

# wally.toml
[dev-dependencies]
Jest = "jsdotlua/jest@3.10.0"
JestGlobals = "jsdotlua/jest-globals@3.10.0"

-- src/shared/Inventory.spec.luau
local ReplicatedStorage = game:GetService("ReplicatedStorage")

local JestGlobals = require(ReplicatedStorage.DevPackages.JestGlobals)
local Inventory = require(ReplicatedStorage.Shared.Inventory)

local describe, it, expect = JestGlobals.describe, JestGlobals.it, JestGlobals.expect

describe("Inventory.add", function()
	it("stacks items up to the limit", function()
		local inventory = {}
		expect(Inventory.add(inventory, "Apple", 3, 5)).toBe(true)
		expect(inventory.Apple).toBe(3)
		local ok, reason = Inventory.add(inventory, "Apple", 3, 5)
		expect(ok).toBe(false)
		expect(reason).toBe("stack full")
	end)

	it("rejects fractional amounts", function()
		expect(Inventory.add({}, "Apple", 0.5, 5)).toBe(false)
	end)
end)

• Put a jest.config.luau (return { testMatch = { "**/*.spec" } }) in each test root.
• Runner script (Studio command bar, a test place Script, or cloud task): require(ReplicatedStorage.DevPackages.Jest).runCLI(root, { ci = true }, { root }):awaitStatus() → inspect result.results.numFailedTests.
• Jest Lua 3 needs the fast flag FFlagEnableLoadModule = true in Studio's ClientAppSettings.json when run locally.
• Map DevPackages into the DataModel only for test builds (separate Rojo project, e.g. test.project.json).

Where tests run

Open Cloud Luau Execution flow (details and a script: references/cloud-test-runner.md):

1. Build the test place (rojo build test.project.json -o test.rbxl) and upload it as a Saved version of a dedicated test place.
2. POST /cloud/v2/universes/{u}/places/{p}/versions/{v}/luau-execution-session-tasks with { "script": ... } (API key scope universe.place.luau-execution-session:write; rate limit ≈ 5 tasks/min per key owner).
3. Poll the task path until state is COMPLETE/FAILED; read output.results and .../logs.

Playtesting in Studio

• Test tab: Play (you + server), Run (server only, no character), Clients and Servers with 2+ players to test replication, trading, and PvP. Most multiplayer bugs only appear with ≥ 2 clients.
• Device Simulator toolbar (Test → Device Simulator, top of the viewport): switch phone/tablet/console mid-playtest, with touch-control hints; its Network Simulator applies 3G/4G/Wi-Fi/wired or custom inbound/outbound latency, jitter, and packet loss to test lag compensation and loading/retry UX. Controller Emulator for gamepad input.
• Streaming: test with StreamingTargetRadius = 64.
• DataStores in Studio: enable API access and use a separate test universe or data store names.

QA checklist before shipping a feature

• Works for a player who joins after the feature started (late joiners), and after respawn.
• Works with 2+ clients; server state is authoritative; UI updates on all clients.
• Player leaving mid-action (trade, purchase, round) leaves no broken state or leaked tables.
• Remotes rejected when spammed or sent malformed arguments.
• Data saves and reloads (rejoin), including teleports between places.
• Mobile, gamepad, and keyboard all work; UI readable on a phone.
• No errors/warnings in Output (server and client).

Related skills

roblox-tooling (CI, Rojo), roblox-studio-mcp (agent-driven playtests), roblox-open-cloud, roblox-code-review.