Make it possible to customize the worker a test is run on.

src/ParallelTestRunner.jl

@@ -1,6 +1,6 @@
 module ParallelTestRunner
 
-export runtests
+export runtests, addworkers, addworker
 
 using Distributed
 using Dates
@@ -213,6 +213,35 @@ function default_njobs(; cpu_threads = Sys.CPU_THREADS, free_memory = Sys.free_m
     return max(1, min(jobs, memory_jobs))
 end
 
+"""
+    addworkers(X; kwargs...)
+
+Add `X` worker processes, with additional keyword arguments passed to `addprocs`.
+"""
+test_exeflags = Base.julia_cmd()
+filter!(test_exeflags.exec) do c
+    return !(startswith(c, "--depwarn") || startswith(c, "--check-bounds"))
+end
+push!(test_exeflags.exec, "--check-bounds=yes")
+push!(test_exeflags.exec, "--startup-file=no")
+push!(test_exeflags.exec, "--depwarn=yes")
+push!(test_exeflags.exec, "--project=$(Base.active_project())")
+test_exename = popfirst!(test_exeflags.exec)
+function addworkers(X; kwargs...)
+    exename = test_exename
+
+    return withenv("JULIA_NUM_THREADS" => 1, "OPENBLAS_NUM_THREADS" => 1) do
+        procs = addprocs(X; exename = exename, exeflags = test_exeflags, kwargs...)
+        Distributed.remotecall_eval(
+            Main, procs, quote
+                import ParallelTestRunner
+            end
+        )
+        procs
+    end
+end
+addworker(; kwargs...) = addworkers(1; kwargs...)[1]
+
 """
     runtests(ARGS; testfilter = Returns(true), RecordType = TestRecord, custom_tests = Dict())
 
@@ -230,6 +259,8 @@ Several keyword arguments are also supported:
 - `custom_tests`: Optional dictionary of custom tests, mapping test names to expressions.
 - `init_code`: Code use to initialize each test's sandbox module (e.g., import auxiliary
   packages, define constants, etc).
+- `test_worker`: Optional function that takes a test name and returns a specific worker.
+  When returning `nothing`, the test will be assigned to any available default worker.
 
 ## Command Line Options
 
@@ -272,7 +303,8 @@ Workers are automatically recycled when they exceed memory limits to prevent out
 issues during long test runs. The memory limit is set based on system architecture.
 """
 function runtests(ARGS; testfilter = Returns(true), RecordType = TestRecord,
-                  custom_tests::Dict{String, Expr}=Dict{String, Expr}(), init_code = :())
+                  custom_tests::Dict{String, Expr}=Dict{String, Expr}(), init_code = :(),
+                  test_worker = Returns(nothing))
     do_help, _ = extract_flag!(ARGS, "--help")
     if do_help
         println(
@@ -372,29 +404,7 @@ function runtests(ARGS; testfilter = Returns(true), RecordType = TestRecord,
     @info "Running $jobs tests in parallel. If this is too many, specify the `--jobs=N` argument to the tests, or set the `JULIA_CPU_THREADS` environment variable."
 
     # add workers
-    test_exeflags = Base.julia_cmd()
-    filter!(test_exeflags.exec) do c
-        return !(startswith(c, "--depwarn") || startswith(c, "--check-bounds"))
-    end
-    push!(test_exeflags.exec, "--check-bounds=yes")
-    push!(test_exeflags.exec, "--startup-file=no")
-    push!(test_exeflags.exec, "--depwarn=yes")
-    push!(test_exeflags.exec, "--project=$(Base.active_project())")
-    test_exename = popfirst!(test_exeflags.exec)
-    function addworker(X; kwargs...)
-        exename = test_exename
-
-        return withenv("JULIA_NUM_THREADS" => 1, "OPENBLAS_NUM_THREADS" => 1) do
-            procs = addprocs(X; exename = exename, exeflags = test_exeflags, kwargs...)
-            Distributed.remotecall_eval(
-                Main, procs, quote
-                    import ParallelTestRunner
-                end
-            )
-            procs
-        end
-    end
-    addworker(min(jobs, length(tests)))
+    addworkers(min(jobs, length(tests)))
 
     # pretty print information about gc and mem usage
     testgroupheader = "Test"
@@ -492,21 +502,21 @@ function runtests(ARGS; testfilter = Returns(true), RecordType = TestRecord,
                     while length(tests) > 0
                         test = popfirst!(tests)
 
-                        # sometimes a worker failed, and we need to spawn a new one
+                        # if a worker failed, spawn a new one
                         if p === nothing
-                            p = addworker(1)[1]
+                            p = addworkers(1)[1]
                         end
-                        wrkr = p
 
-                        local resp
+                        # some tests may need a special worker
+                        wrkr = something(test_worker(test), p)
 
                         # run the test
                         running_tests[test] = now()
-                        try
-                            resp = remotecall_fetch(runtest, wrkr, RecordType, test_runners[test], test, init_code)
+                        resp = try
+                            remotecall_fetch(runtest, wrkr, RecordType, test_runners[test], test, init_code)
                         catch e
                             isa(e, InterruptException) && return
-                            resp = Any[e]
+                            Any[e]
                         end
                         delete!(running_tests, test)
                         push!(results, (test, resp))
@@ -529,6 +539,11 @@ function runtests(ARGS; testfilter = Returns(true), RecordType = TestRecord,
                             # so future tests get a fresh environment
                             p = recycle_worker(p)
                         end
+
+                        # get rid of the custom worker
+                        if wrkr != p
+                            recycle_worker(wrkr)
+                        end
                     end
 
                     if p !== nothing

test/runtests.jl

@@ -20,3 +20,20 @@ custom_tests = Dict(
     end
 )
 runtests(ARGS; init_code, custom_tests)
+
+# custom worker
+function test_worker(name)
+    if name == "needs env var"
+        return addworker(env=["SPECIAL_ENV_VAR"=>"42"])
+    end
+    return nothing
+end
+custom_tests = Dict(
+    "needs env var" => quote
+        @test ENV["SPECIAL_ENV_VAR"] == "42"
+    end,
+    "doesn't need env var" => quote
+        @test !haskey(ENV, "SPECIAL_ENV_VAR")
+    end
+)
+runtests(ARGS; test_worker, custom_tests)