lsp-test: Functional test framework for LSP servers.

[ bsd3, library, testing ] [ Propose Tags ]

A test framework for writing tests against Language Server Protocol servers. Language.Haskell.LSP.Test launches your server as a subprocess and allows you to simulate a session down to the wire, and Language.Haskell.LSP.Test can replay captured sessions from It's currently used for testing in haskell-ide-engine.

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Change log
Dependencies aeson, aeson-pretty, ansi-terminal, async, base (>=4.10 && <5), bytestring, conduit, conduit-parse (>=0.2 && <0.3), containers, data-default, Diff, directory, filepath, haskell-lsp (>=0.16 && <0.17), lens, mtl (<2.3), parser-combinators, process, rope-utf16-splay, text, transformers, unix, unordered-containers, Win32 [details]
License BSD-3-Clause
Copyright 2019 Luke Lau
Author Luke Lau
Revised Revision 1 made by sjakobi at 2022-05-11T10:25:08Z
Category Testing
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Source repo head: git clone
Uploaded by luke_ at 2019-09-08T21:07:23Z
Distributions Arch:, LTSHaskell:, NixOS:, Stackage:
Reverse Dependencies 4 direct, 0 indirect [details]
Downloads 30439 total (221 in the last 30 days)
Rating 2.0 (votes: 1) [estimated by Bayesian average]
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Status Docs available [build log]
Last success reported on 2019-09-08 [all 1 reports]

Readme for lsp-test-

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lsp-test Build Status Hackage

lsp-test is a functional testing framework for Language Server Protocol servers.

import Language.Haskell.LSP.Test
runSession "hie" fullCaps "proj/dir" $ do
  doc <- openDoc "Foo.hs" "haskell"
  skipMany anyNotification
  symbols <- getDocumentSymbols doc


Unit tests with HSpec

describe "diagnostics" $
  it "report errors" $ runSession "hie" fullCaps "test/data" $ do
    openDoc "Error.hs" "haskell"
    [diag] <- waitForDiagnosticsSource "ghcmod"
    liftIO $ do
      diag ^. severity `shouldBe` Just DsError
      diag ^. source `shouldBe` Just "ghcmod"

Replaying captured session

replaySession "hie" "test/data/renamePass"

Parsing with combinators

skipManyTill loggingNotification publishDiagnosticsNotification
count 4 (message :: Session ApplyWorkspaceEditRequest)
anyRequest <|> anyResponse

Try out the example tests in the example directory with cabal new-test. For more examples check the Wiki


The tests are integration tests, so make sure you have the following language servers installed and on your PATH:


  • Check out a relatively recent version of the repo, or see .travis.yml to get the exact commit used for CI.
  • stack install


npm i -g javascript-typescript-langserver

Then run the tests with stack test or cabal new-test.