Ansible on it's own doesn't have a convenient way to preview what templates will be rendered as. Luckily there's an online tool to help with that:
Ansible provides a tool that checks your ansible files for best practices.
To lint a specific file or automagically detect what to lint:
ansible-lint ansible-lint
If using vim, the following snippet can be used to run ansible-lint inside the editor. By running :make, all the ansible-lint errors will be pulled into vim's quickfix list:
autocmd BufRead,BufNewFile *.ymlyml
\ set makeprg=ansible-lint\ -p errorformat=%f:%l:\ [E%n]\ %m,%f:%l:\ [EANSIBLE%n]\ %m,%f:%l:\ [ANSIBLE%n]\ %m,%f:%l:%c:\ %m,%f:%l:\ %m
note: this changes makeprg & errorformat for all yml files which might not be what you want