install mpi4py for mpi tests

Author: minrk

.github/workflows/test.yml

@@ -59,21 +59,23 @@ jobs:
             ~/conda
           key: conda
 
-      - name: install MPI
+      - name: Install Python (conda) ${{ matrix.python }}
         if: matrix.mpi
         run: |
           export MAMBA_ROOT_PREFIX=$HOME/conda
           test -d $MAMBA_ROOT_PREFIX || mkdir $MAMBA_ROOT_PREFIX
           wget -qO- https://micro.mamba.pm/api/micromamba/linux-64/latest | tar -xvj bin/micromamba
           eval "$(./bin/micromamba shell hook -s posix)"
           micromamba activate
-          micromamba install -y -c conda-forge mpich
+          micromamba install -y -c conda-forge mpich mpi4py python=${{ matrix.python }}
           echo "PATH=$MAMBA_ROOT_PREFIX/bin:$PATH" >> $GITHUB_ENV
 
       - name: Install Python ${{ matrix.python }}
+        if: ${{ ! matrix.mpi }}
         uses: actions/setup-python@v2
         with:
           python-version: ${{ matrix.python }}
+
       - name: Install Python dependencies
         run: |
           pip install --upgrade pip