Remove race condition in mpi testing (#1821)

* remove race condition in mpi testing

* add additional barriers

test/test_mpi.jl

@@ -8,6 +8,7 @@ include("test_trixi.jl")
 # Start with a clean environment: remove Trixi.jl output directory if it exists
 outdir = "out"
 Trixi.mpi_isroot() && isdir(outdir) && rm(outdir, recursive = true)
+Trixi.MPI.Barrier(Trixi.mpi_comm())
 
 # CI with MPI and some tests fails often on Windows. Thus, we check whether this
 # is the case here. We use GitHub Actions, so we can check whether we run CI
@@ -45,5 +46,6 @@ end # MPI supporting functionality
 
 # Clean up afterwards: delete Trixi.jl output directory
 Trixi.mpi_isroot() && @test_nowarn rm(outdir, recursive = true)
+Trixi.MPI.Barrier(Trixi.mpi_comm())
 
 end # module

test/test_mpi_tree.jl

@@ -76,7 +76,8 @@ CI_ON_WINDOWS = (get(ENV, "GITHUB_ACTIONS", false) == "true") && Sys.iswindows()
         # Here, we also test that SaveSolutionCallback prints multiple mesh files with AMR
         # Start with a clean environment: remove Trixi.jl output directory if it exists
         outdir = "out"
-        isdir(outdir) && rm(outdir, recursive = true)
+        Trixi.mpi_isroot() && isdir(outdir) && rm(outdir, recursive = true)
+        Trixi.MPI.Barrier(Trixi.mpi_comm())
         @test_trixi_include(joinpath(EXAMPLES_DIR,
                                      "elixir_advection_amr_refine_twice.jl"),
                             l2=[0.00020547512522578292],

test/test_threaded.jl

@@ -8,6 +8,7 @@ include("test_trixi.jl")
 # Start with a clean environment: remove Trixi.jl output directory if it exists
 outdir = "out"
 Trixi.mpi_isroot() && isdir(outdir) && rm(outdir, recursive = true)
+Trixi.MPI.Barrier(Trixi.mpi_comm())
 
 @testset "Threaded tests" begin
 #! format: noindent
@@ -471,5 +472,6 @@ end
 
 # Clean up afterwards: delete Trixi.jl output directory
 Trixi.mpi_isroot() && isdir(outdir) && @test_nowarn rm(outdir, recursive = true)
+Trixi.MPI.Barrier(Trixi.mpi_comm())
 
 end # module