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.LSP.Test launches your server as a subprocess and allows you to simulate a session down to the wire. To see examples of it in action, check out haskell-ide-engine, haskell-language-server and ghcide.

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[Last Documentation]

  • Control
    • Applicative
      • Control.Applicative.Combinators
  • Language
    • LSP
      • Protocol
        • Language.LSP.Protocol.Capabilities
        • Language.LSP.Protocol.Message
        • Language.LSP.Protocol.Types
      • Language.LSP.Test


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Change log
Dependencies aeson, aeson-pretty, ansi-terminal, async (>=2.0), base (>=4.10 && <5), bytestring, co-log-core, conduit, conduit-parse (>=0.2 && <0.3), containers (>=0.5.9), data-default, Diff (>=0.3), directory, exceptions, filepath, Glob (>=0.9 && <0.11), lens, lsp (>=2.0 && <2.1), lsp-types (>=2.0 && <2.1), mtl (<2.4), parser-combinators (>=1.2), process (>=1.6), row-types, some, text, time, transformers, unix, Win32 [details]
License BSD-3-Clause
Copyright 2021 Luke Lau
Author Luke Lau
Category Testing
Home page
Bug tracker
Source repo head: git clone
Uploaded by michaelpj at 2023-06-14T16:10:21Z
Distributions Arch:, LTSHaskell:, NixOS:, Stackage:
Reverse Dependencies 4 direct, 0 indirect [details]
Downloads 32157 total (250 in the last 30 days)
Rating 2.0 (votes: 1) [estimated by Bayesian average]
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Status Docs not available [build log]
All reported builds failed as of 2023-06-14 [all 2 reports]

Readme for lsp-test-

[back to package description]


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

It is part of the lsp family of packages, along with lsp and lsp-types

import Language.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 see this introductory blog post.

Whilst writing your tests you may want to debug them to see what's going wrong. You can set the logMessages and logStdErr options in SessionConfig to see what the server is up to. There are also corresponding environment variables so you can turn them on from the command line:



The tests for lsp-test use a dummy server found in test/dummy-server/. Run the tests with cabal test or stack test. Tip: If you want to filter the tests, use cabal run test:tests -- -m "foo"


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.