Add missing tests for Messenger

tests/test_Messenger.cpp

 #include <catch2/catch_test_macros.hpp>
 #include <catch2/matchers/catch_matchers_all.hpp>
 
+#include <algebra/TinyVector.hpp>
 #include <utils/Array.hpp>
 #include <utils/Messenger.hpp>
 
@@ -143,6 +144,14 @@ TEST_CASE("Messenger", "[mpi]")
 
     const bool or_value_2 = parallel::allReduceOr(parallel::rank() > 0);
     REQUIRE(or_value_2 == (parallel::size() > 1));
+
+    const size_t sum_value = parallel::allReduceSum(parallel::rank() + 1);
+    REQUIRE(sum_value == parallel::size() * (parallel::size() + 1) / 2);
+
+    const TinyVector<2, size_t> sum_tiny_vector =
+      parallel::allReduceSum(TinyVector<2, size_t>(parallel::rank() + 1, 1));
+    REQUIRE(
+      (sum_tiny_vector == TinyVector<2, size_t>{parallel::size() * (parallel::size() + 1) / 2, parallel::size()}));
   }
 
   SECTION("all to all")