How can I test functions inside a single file Lua script?

I would like to unit test functions from a single file Lua script, say script.lua. Let's say I do not want to separate the functions from the script file into a separate module file (which would probably make things easier). How can I define tests (preferably with luaunit because easy to integrate, but other tool would be ok as well) for the functions defined in script.lua inside the script.lua file or in a separate test_script.lua file?