Restore the working project after running user code.

[maleadt]

Otherwise the runner is broken after a test switches projects:

using ParallelTestRunner
using Test

testsuite = Dict(
    "first test" => quote
        using Pkg
        Pkg.activate(; temp=true)
        @test 1 + 1 == 2
    end,
    "second test" => quote
        @test 2 * 2 == 4
    end
)

runtests(ParallelTestRunner, ["--verbose", "--jobs=1"]; testsuite)

                  │          │ ──────────────── CPU ──────────────── │
Test     (Worker) │ Time (s) │ GC (s) │ GC % │ Alloc (MB) │ RSS (MB) │
first test    (1) │        started at 2026-02-23T10:26:32.874
first test    (1) │     0.21 │   0.00 │  0.0 │      30.71 │   378.98 │
second test   (1) │        started at 2026-02-23T10:26:34.700
second test   (1) |         crashed at 2026-02-23T10:26:35.219

Output generated during execution of 'first test':
┌ Precompiling packages...
│     502.1 ms  ✓ ParallelTestRunner
│   1 dependency successfully precompiled in 1 seconds. 35 already precompiled.
└   Activating new project at `/var/folders/wc/z_cydqs118735x03cvsf96tr0000gn/T/jl_5Vo7BU`

Test Summary:   | Pass  Error  Total  Time
  Overall       |    1      1      2  5.2s
    first test  |    1             1  0.2s
    second test |           1      1  0.5s
    FAILURE

Error in testset second test:
Error During Test at none:1
  Got exception outside of a @test
  Remote exception from Malt.Worker on port 9179 with PID 42179:
  
  ArgumentError: Package ParallelTestRunner not found in current path, maybe you meant `import/using .ParallelTestRunner`.
  - Otherwise, run `import Pkg; Pkg.add("ParallelTestRunner")` to install the ParallelTestRunner package.
  Stacktrace:
   [1] macro expansion
     @ ./loading.jl:2403 [inlined]
   [2] macro expansion
     @ ./lock.jl:376 [inlined]
   [3] __require(into::Module, mod::Symbol)
     @ Base ./loading.jl:2386
   [4] require(into::Module, mod::Symbol)
     @ Base ./loading.jl:2362
   [5] eval(m::Module, e::Any)
     @ Core ./boot.jl:489
   [6] (::var"#handle##0#handle##1"{Sockets.TCPSocket, UInt64, Bool, @Kwargs{}, Tuple{Module, Expr}, typeof(Core.eval)})()
     @ Main ~/.julia/packages/Malt/yA40d/src/worker.jl:120
ERROR: LoadError: Test run finished with errors
in expression starting at /Users/tim/Julia/pkg/ParallelTestRunner/wip.jl:15

Also add workspace entries for 1.12.

[vchuravy]

Hm, elsewhere (as an example in Base) it is the responsibility of the party modifying the state to reset it.

function precompile_test_harness(@nospecialize(f), testset::String)
    @testset "$testset" precompile_test_harness(f, true)
end
function precompile_test_harness(@nospecialize(f), separate::Bool=true)
    load_path = mkdepottempdir()
    load_cache_path = separate ? mkdepottempdir() : load_path
    try
        pushfirst!(LOAD_PATH, load_path)
        pushfirst!(DEPOT_PATH, load_cache_path)
        f(load_path)
    finally
        filter!((≠)(load_path), LOAD_PATH)
        separate && filter!((≠)(load_cache_path), DEPOT_PATH)
    end
    return nothing
end

Beside the active project, there is also depot path and load path

[maleadt]

So the use case here is running examples, which often start with a Pkg.activate(@__DIR__). I guess I could add this to my harness executing examples, but it seemed reasonable to make ParallelTestRunner more robust to that.