message: add host operation test
diff: @@ -104,6 +104,21 @@ TEST_F(Executor, RunsCorrectOperation)
  }
  +void host_operation(int& value) { value = 1234; }
  +
  +GKO_REGISTER_HOST_OPERATION(host_operation, host_operation);
  +
  +
  +TEST_F(Executor, RunsCorrectHostOperation)
  +{
  + int value = 0;
  +
  + exec->run(make_host_operation(value));
  +
  + ASSERT_EQ(1234, value);
  +}
  +
  +
  #ifndef GKO_COMPILING_REFERENCE
  