From 45b1e820a359cb30bf16425a411cd64892922d46 Mon Sep 17 00:00:00 2001
From: Alexander Nesterov <nesterov.alexander@outlook.com>
Date: Thu, 6 Nov 2025 18:25:27 +0100
Subject: [PATCH] ensure deterministic test shuffle order across MPI ranks

---
 modules/runners/src/runners.cpp | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/modules/runners/src/runners.cpp b/modules/runners/src/runners.cpp
index e1385287..df735d8e 100644
--- a/modules/runners/src/runners.cpp
+++ b/modules/runners/src/runners.cpp
@@ -3,10 +3,13 @@
 #include <gtest/gtest.h>
 #include <mpi.h>
 
+#include <chrono>
+#include <cstdint>
 #include <cstdlib>
 #include <format>
 #include <iostream>
 #include <memory>
+#include <random>
 #include <stdexcept>
 #include <string>
 
@@ -88,6 +91,26 @@ int Init(int argc, char **argv) {
 
   ::testing::InitGoogleTest(&argc, argv);
 
+  // Ensure consistent GoogleTest shuffle order across all MPI ranks.
+  unsigned int seed = 0;
+  int rank_for_seed = -1;
+  MPI_Comm_rank(MPI_COMM_WORLD, &rank_for_seed);
+
+  if (rank_for_seed == 0) {
+    try {
+      seed = std::random_device{}();
+    } catch (...) {
+      seed = 0;
+    }
+    if (seed == 0) {
+      const auto now = static_cast<std::uint64_t>(std::chrono::steady_clock::now().time_since_epoch().count());
+      seed = static_cast<unsigned int>(((now & 0x7fffffffULL) | 1ULL));
+    }
+  }
+
+  MPI_Bcast(&seed, 1, MPI_UNSIGNED, 0, MPI_COMM_WORLD);
+  ::testing::GTEST_FLAG(random_seed) = static_cast<int>(seed);
+
   auto &listeners = ::testing::UnitTest::GetInstance()->listeners();
   int rank = -1;
   MPI_Comm_rank(MPI_COMM_WORLD, &rank);