tests(ui): add unit tests for UI functionality

[vyskocilm]

No description provided.

[vyskocilm]

I spent some time experimenting with a various approaches towards the testing of UI. I think that going full functional with a msgpack and remote headless instance is not necessary and the testing can stay on unit level with stubs. There's no need to test things like curl, jq or http servers either :-).

However as internal helpers like close_buffer can't be mocked and call two vim functions already. The development experience of mocking the second level dependencies. This leads to ugly code. The worst case scenario is to have tests which will be removed in a case of code refactoring.

I've checked documentation of a busted https://lunarmodules.github.io/busted/#private - but exporting the helpers for tests does not help at all. I believe this is a good match between testability and a readability of the resulting tests.

WDYT?

[rcasia]

Check the tests from https://github.com/tris203/precognition.nvim. They are pretty good. They make tests based on the buffers.

This would be an example for this PR:

----- utility functions
  ---@param lines string[]
  ---@return integer bufnr
  local create_buf = function(lines)
    local bufnr = vim.api.nvim_create_buf(true, true)
    vim.api.nvim_buf_set_lines(bufnr, 0, -1, false, lines)
    vim.api.nvim_set_current_buf(bufnr)
    vim.api.nvim_win_set_cursor(0, { 1, 1 })

    return bufnr
  end


  ---@param bufnr integer
  ---@return string[] lines
  local get_buf_lines = function(bufnr)
    return vim.api.nvim_buf_get_lines(bufnr, 0, -1, false)
  end

----- actual test
  it("from_curl (revised)", function()
    local bufnr = create_buf({}) -- empty buffer
    vim.fn.setreg("+", "curl http://example.com")

    UI.from_curl()

    local expected = {
      [[# curl http://example.com]],
      [[GET http://example.com]],
      [[]],
      [[]],
    }
    assert.are.same(expected, get_buf_lines(bufnr))
  end)

(Those first functions could be on a test utility module)

[vyskocilm]

@rcasia amazing approach. Love it more than the heavy mocking. The more I thought about this PR the less I wanted to work on it. This looks like a great compromise between fully functional tests via headless neovim and more approachable unit testing.

[vyskocilm]

A backward compatibility ... did not want to touch everything for a draft PR

[gorillamoe]

I think we really need more tests and so this is a real good addition. Thanks for your efforts @vyskocilm!

[rcasia]

I'd be happy to continue the PR if needed.

[vyskocilm]

@rcasia

I'd be happy to continue the PR if needed.

I'd say your approach is superior, so lets close this PR. There's a little value.

[rcasia]

Nice! Let me continue the work tomorrow. I'll continue this same branch.

[rcasia]

Continued in #266