Testing Our Code

Testing allows us to ensure that our code behaves as expected and that we don't introduce regressions when making changes. In this chapter, we'll learn how to write tests for our Lua code.

Testing Framework

In Lua, testing is primarily done using the busted testing framework. Lux takes care of installing busted for you when running tests!

Restructuring Our Project

To start testing our code, we need to restructure our project a little. First, let's move out our newly made has_hello function into its own file. Create a new file called src/has_hello.lua and move the function there:

src/has_hello.lua

--- Checks whether input has the word "hello"
---@param input string
local function has_hello(input)
    return input:lower():find("hello") ~= nil
end

return {
    has_hello = has_hello,
}

Next, let's update our main.lua file to use this new file:

src/main.lua

local has_hello = require("has_hello").has_hello
local argparse = require("argparse")

-- Create an argument parser
local parser = argparse("script", "An example.")
parser:argument("input", "Input file.")

local args = parser:parse()

-- Directly print out the "input" argument
if has_hello(args.input) then
    print("Your input has the word 'hello' in it!")
else
    print("Your input does not have the word 'hello' in it!")
end

Writing our First Test

Now that we have our code structured, let's write our first test. Tests are usually stored in a spec/ directory, and each test file must end in _spec.lua. Create a new directory called spec/ in the root of your project:

mkdir spec

Inside the spec/ directory, create a new file called has_hello_spec.lua:

spec/has_hello_spec.lua

local has_hello = require("has_hello").has_hello

describe("has_hello", function()
    it("should return true if input has the word 'hello'", function()
        assert.is_true(has_hello("hello world"))
    end)

    it("should return false if input does not have the word 'hello'", function()
        assert.is_false(has_hello("world"))
    end)
end)

Running the Tests

We're now ready to run our tests! lx test will run all the tests in your project. After the automatic installation of busted you should see the following output:

lx test

●●
2 successes / 0 failures / 0 errors / 0 pending : 0.001615 seconds

If so, congratulations! You've successfully written and ran your first test!