Test item runner doesn't work in vscode

General Usage
,
1

I recently switched one of my projects to use the new Workspace organization with the main project and test as separate projects in the workspace. Now I get an error when I try to run the tests using the test item runner in VSCode:

ERROR: can not merge projects
Stacktrace:
 [1] pkgerror(msg::String)
   @ Pkg.Types C:\Users\seatt\.julia\juliaup\julia-1.12.4+0.x64.w64.mingw32\share\julia\stdlib\v1.12\Pkg\src\Types.jl:68
 [2] activate(pkg::String; allow_reresolve::Bool)
   @ TestItemServer.TestEnv c:\Users\seatt\.vscode\extensions\julialang.language-julia-1.171.2\scripts\packages\TestItemControllers\packages\TestEnv\src\julia-1.11\activate_set.jl:44
 [3] activate
   @ c:\Users\seatt\.vscode\extensions\julialang.language-julia-1.171.2\scripts\packages\TestItemControllers\packages\TestEnv\src\julia-1.11\activate_set.jl:9 [inlined]
 [4] activate_env_request(params::TestItemServer.TestItemServerProtocol.ActivateEnvParams, state::TestItemServer.TestProcessState{var"#2#3"}, token::TestItemServer.CancellationTokens.CancellationToken)
   @ TestItemServer c:\Users\seatt\.vscode\extensions\julialang.language-julia-1.171.2\scripts\packages\TestItemControllers\testprocess\TestItemServer\src\TestItemServer.jl:572
 [5] dispatch_msg(x::TestItemServer.JSONRPC.JSONRPCEndpoint{Base.PipeEndpoint, Base.PipeEndpoint}, msg::TestItemServer.JSONRPC.Request, context::TestItemServer.TestProcessState{var"#2#3"})
   @ TestItemServer c:\Users\seatt\.vscode\extensions\julialang.language-julia-1.171.2\scripts\packages\TestItemControllers\packages\JSONRPC\src\typed.jl:114
 [6] (::TestItemServer.var"#serve##2#serve##3"{TestItemServer.TestProcessState{var"#2#3"}, TestItemServer.JSONRPC.JSONRPCEndpoint{Base.PipeEndpoint, Base.PipeEndpoint}, TestItemServer.JSONRPC.Request})()
   @ TestItemServer c:\Users\seatt\.vscode\extensions\julialang.language-julia-1.171.2\scripts\packages\TestItemControllers\testprocess\TestItemServer\src\TestItemServer.jl:731

Tests run fine from the package manager mode in the REPL.

This just started happening. Is there a configuration file I have to change to fix this? Or does VSCode not yet work with Workspaces?

Version info:

Julia Version 1.12.4
Commit 01a2eadb04 (2026-01-06 16:56 UTC)
Build Info:
  Official https://julialang.org release
Platform Info:
  OS: Windows (x86_64-w64-mingw32)
  CPU: 32 × AMD Ryzen 9 7950X 16-Core Processor
  WORD_SIZE: 64
  LLVM: libLLVM-18.1.7 (ORCJIT, znver4)
  GC: Built with stock GC
Threads: 16 default, 1 interactive, 16 GC (on 32 virtual cores)
Environment:
  JULIA_EDITOR = code.cmd
  JULIA_NUM_THREADS = 16

vscode version:

Version: 1.108.0 (user setup)
Commit: 94e8ae2b28cb5cc932b86e1070569c4463565c37
Date: 2026-01-08T13:53:10.781Z
Electron: 39.2.7
ElectronBuildId: 12953945
Chromium: 142.0.7444.235
Node.js: 22.21.1
V8: 14.2.231.21-electron.0
OS: Windows_NT x64 10.0.26200
2

I think I’ve been running into the same issue. I’m not an expert on that codebase but my impression is that it’s a bug with a fix in progress.

I’ve added some thoughts to the following issue: `@testitem` encounters ERROR: can not merge projects · Issue #3921 · julia-vscode/julia-vscode · GitHub