[Tests] Added parallel grid tests using MPI if available

(cherry picked from commit df0eb79d6374e2bd057cc6e7be17322649901c28)

dune/grid/test/yasp/CMakeLists.txt

 
+# add test include property manually because the folder is not called "test"
+set_property(DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
+  PROPERTY TEST_INCLUDE_FILE ${CMAKE_CURRENT_BINARY_DIR}/BuildTests.cmake)
+
 set(TESTS
   test-yaspgrid-backuprestore
   test-yaspgrid-tensorgridfactory
@@ -16,14 +20,29 @@ foreach(_test ${TESTS})
   add_test(${_test} ${_test})
 endforeach(_test ${TESTS})
 
-# add test include property manually because the folder is not called "test"
-set_property(DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
-  PROPERTY TEST_INCLUDE_FILE ${CMAKE_CURRENT_BINARY_DIR}/BuildTests.cmake)
-
 # Add tests to test target
 add_directory_test_target(_test_target)
 add_dependencies(${_test_target} ${TESTS})
 
+# If we have MPI, include parallel tests
+if(MPI_FOUND)
+
+  set(TESTS_PARALLEL
+    test-yaspgrid-backuprestore
+    test-yaspgrid-tensorgridfactory
+    test-yaspgrid-yaspfactory-1d
+    test-yaspgrid-yaspfactory-2d
+    test-yaspgrid-yaspfactory-3d
+  )
+
+  # Create tests with mpi command and add them to the test target
+  foreach(_test ${TESTS_PARALLEL})
+    add_test(NAME ${_test}_parallel
+      COMMAND ${MPIEXEC} ${MPIEXEC_NUMPROC_FLAG} "2" ${_test})
+    add_dependencies(${_test_target} ${_test}_parallel)
+  endforeach(_test ${TESTS_PARALLEL})
+
+endif(MPI_FOUND)
 
 set(SOURCES
   test-yaspgrid-backuprestore.cc