My GSoC 2018 project (and first package!), lsp-test https://hackage.haskell.org/package/lsp-test-0.1.0.0, is now available on Hackage. It allows you to carry out functional end-to-end tests at a high level for LSP https://microsoft.github.io/language-server-protocol/ servers, and we’re currently using it in haskell-ide-engine https://github.com/haskell/haskell-ide-engine. Many thanks to Alan Zimmerman and Zubin Duggal for their invaluable help this summer. Hopefully it will help improve your LSP servers, or maybe entice you to make one for your language!