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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Dependencies aeson, aeson-pretty, ansi-terminal, async, base (>=4.10 && <5), bytestring, conduit, conduit-parse (>=0.2 && <0.3), containers (>=0.5.9), data-default, Diff, directory, filepath, haskell-lsp (>=0.22 && <0.23), lens, mtl (<2.3), parser-combinators (>=1.2), process (>=1.6), 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 2022-05-11T10:25:10Z
Category Testing
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Source repo head: git clone
Uploaded by luke_ at 2020-05-04T18:59:26Z
Distributions Arch:, LTSHaskell:, NixOS:, Stackage:
Reverse Dependencies 4 direct, 0 indirect [details]
Downloads 32007 total (362 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 2020-05-04 [all 1 reports]

Readme for lsp-test-

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lsp-test Actions Status Hackage

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

import Language.Haskell.LSP.Test
main = 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 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 cabal test or stack test.


Seeing funny stuff when running lsp-test via stack? If your server is built upon Haskell tooling, keep in mind that stack sets some environment variables related to GHC, and you may want to unset them.