Plenary test for callback function

Plugin Development
1

Hi,

I am writing a new plugin and attempting to write some unit tests for it.

One of my functions uses vim.ui.select, which takes a list of selection options and a callback as parameters. The selection is used as an argument for the callback function. Here is the example from the help docs:

vim.ui.select({ 'tabs', 'spaces' }, {
           prompt = 'Select tabs or spaces:',
           format_item = function(item)
               return "I'd like to choose " .. item
           end,
       }, function(choice)
           if choice == 'spaces' then
               vim.o.expandtab = true
           else
               vim.o.expandtab = false
           end
       end)

My question is, how would I test this? I’ve tried using mocks and spies with the luassert/plenary to no avail. To make matters worse, I’m 3 functions deep in callback hell. I’d prefer to use vim.ui.select because of the nice telescope integration, but if I can’t test it properly I’ll be stubborn enough to fallback to something synchronous instead.

Specifically what I’m after is this:

  • Ability to mock a selection, e.g. the first call selects response_a and the second (nested) call selects response_b
  • Ability to assert a function call that happens in the final callback

Any advice would be much appreciated; I’ve tried everything I can think of. I’m struggling with lack of documentation and difficulty finding examples.

Thanks!

2

Could this work?:

local select=vim.ui.select
function vim.ui.select(items, opts, on_choice)
    if opts.choice then
        --NOTE: opts.choice is the index of the item not the item itself
        vim.schedule(function() on_choice(items[opts.choice],opts.choice) end)
    else
        select(items,opts,on_choice)
    end
end
local stat,ret=pcall(test)
vim.ui.select=select
if not stat then error(ret) end
3

Could you define the callback separately and only test that? That would probably make the selection trivial and you don’t need to test that.