We display the detailed info text in the preview window. Vim's preview window is
designed to display actual files, not scratch data. Our approach is to open a
temporary file, even though that file is never written. This way, all of Vim's
existing settings for the preview window (and people's configured mappings) just
work. This is also consistent with showing the documentation in the preview
window during completion.
Other plugins have more complicated functions for this (such as eclim), or
Scratch.vim, but this approach is simple and doesn't require external
dependencies or additional settings.
Tests:
This required fixing a sort-of-bug in which the mock'd Vim module was always
only set once, and could not be changed outside of the module which created it.
This meant that it wasn't easy to have arbitrary tests, because it was dependent
on the order in which the tests execute as to whether the return from
MockVimModule() was actually the one in use.
The solution was to make the mock'd vim module a singleton, and use mock's
patch decorator to assign new MagicMock() instances to those methods in the vim
module which a particular test is interested in.
