Adding multiprocess unit tests (#312)

Adding multiprocess unit tests for collectives.  

To run, NCCL_COMM_ID=$HOSTNAME:12345 build/release/test/UnitTestsMultiProcess

test/test_AllToAllMultiProcess.hpp

@@ -0,0 +1,53 @@
+/*************************************************************************
+ * Copyright (c) 2019-2021 Advanced Micro Devices, Inc. All rights reserved.
+ *
+ * See LICENSE.txt for license information
+ ************************************************************************/
+#ifndef TEST_ALLTOALL_MULTI_PROCESS_HPP
+#define TEST_ALLTOALL_MULTI_PROCESS_HPP
+
+#include "CorrectnessTest.hpp"
+
+namespace CorrectnessTests
+{
+    class AllToAllMultiProcessCorrectnessTest : public MultiProcessCorrectnessTest
+    {
+    public:
+        static void ComputeExpectedResults(Dataset& dataset, int const rank)
+        {
+            for (int i = 0; i < dataset.numDevices; i++)
+            {
+                HIP_CALL(hipMemcpy((int8_t *)dataset.expected[i]+dataset.NumBytes()*rank, (int8_t *)dataset.inputs[rank]+dataset.NumBytes()*i,
+                               dataset.NumBytes(), hipMemcpyDeviceToHost));
+            }
+        }
+
+        void TestAllToAll(int rank, Dataset& dataset)
+        {
+            SetUpPerProcess(rank, ncclCollAllToAll, comms[rank], streams[rank], dataset);
+
+            if (numDevices > numDevicesAvailable) return;
+
+            // Prepare input / output / expected results
+            FillDatasetWithPattern(dataset, rank);
+            ComputeExpectedResults(dataset, rank);
+
+            // Launch the reduction
+            ncclAllToAll(dataset.inputs[rank],
+                         dataset.outputs[rank],
+                         numElements, dataType,
+                         comms[rank], streams[rank]);
+
+            // Wait for reduction to complete
+            HIP_CALL(hipStreamSynchronize(streams[rank]));
+
+            // Check results
+            ValidateResults(dataset, rank);
+
+            TearDownPerProcess(comms[rank], streams[rank]);
+            dataset.Release(rank);
+        }
+    };
+}
+
+#endif