Refuse to reduce if global array is empty (send_counts all 0) (#726)

include/kamping/plugin/reproducible_reduce.hpp

@@ -536,6 +536,8 @@ class ReproducibleReducePlugin
             );
         }
 
+        KASSERT(global_array_length > 0, "The array must not be empty");
+
         // Construct index map which maps global array indices to PEs
         std::map<size_t, size_t> start_indices;
         for (size_t p = 0; p < comm.size(); ++p) {

tests/plugins/reproducible_reduce.cpp

@@ -330,7 +330,7 @@ TEST(ReproducibleReduceTest, Fuzzing) {
     }
     comm.bcast_single(kamping::send_recv_buf(seed));
 
-    std::uniform_int_distribution<size_t> array_length_distribution(0, 20);
+    std::uniform_int_distribution<size_t> array_length_distribution(1, 20);
     std::uniform_int_distribution<size_t> rank_distribution(1, comm.size());
     std::mt19937                          rng(seed);       // RNG for distribution & rank number
     std::mt19937                          rng_root(rng()); // RNG for data generation (out-of-sync with other ranks)
@@ -340,6 +340,7 @@ TEST(ReproducibleReduceTest, Fuzzing) {
     for (auto i = 0U; i < NUM_ARRAYS; ++i) {
         std::vector<double> data_array;
         size_t const        data_array_size = array_length_distribution(rng);
+        ASSERT_NE(0, data_array_size);
         if (comm.is_root()) {
             data_array = generate_test_vector(data_array_size, rng_root());
         }
@@ -513,6 +514,15 @@ TEST(ReproducibleReduceTest, ErrorChecking) {
             ),
             ""
         );
+
+        // Empty array, send_counts all zero
+        EXPECT_KASSERT_FAILS(
+            sub_comm.template make_reproducible_comm<double>(
+                kamping::send_counts({0, 0, 0}),
+                kamping::recv_displs({0, 0, 0})
+            ),
+            ""
+        );
     });
 }
 #endif