[fix] Lack of HorovodJoin CPU kernels when install Horovod with NCCL, which make unable to run horovod_sync_train_test.

Author: MoFHeka

tools/testing/build_and_run_tests.sh

@@ -46,8 +46,20 @@ if ! [ -x "$(command -v nvidia-smi)" ]; then
   EXTRA_ARGS="-n auto"
 fi
 
+# Lack of HorovodJoin CPU kernels when install Horovod with NCCL
+if [ "$(uname)" != "Darwin" ]; then
+  # Mac only with MPI
+  python -m pip uninstall horovod -y
+  bash /install/install_horovod.sh $HOROVOD_VERSION --only-cpu
+fi
 # TODO(jamesrong): Test on GPU.
 CUDA_VISIBLE_DEVICES="" mpirun -np 2 -H localhost:2 --allow-run-as-root pytest -v ./tensorflow_recommenders_addons/dynamic_embedding/python/kernel_tests/horovod_sync_train_test.py
+# Reinstall Horovod after tests
+if [ "$(uname)" != "Darwin" ]; then
+  # Mac only with MPI
+  python -m pip uninstall horovod -y
+  bash /install/install_horovod.sh $HOROVOD_VERSION
+fi
 
 # Only use GPU 0 if available.
 if [ -x "$(command -v nvidia-smi)" ]; then