fix nompi builds

Author: franzpoeschel

test/ParallelIOTest.cpp

@@ -36,6 +36,16 @@
 #include <catch2/catch_test_macros.hpp>
 #include <catch2/matchers/catch_matchers_string.hpp>
 
+#if !openPMD_HAVE_MPI
+#define PARALLEL_TEST_CASE(name, tags) TEST_CASE(#name, tags)
+
+PARALLEL_TEST_CASE(none, "[parallel]")
+{}
+
+#else
+
+#include <mpi.h>
+
 #define PARALLEL_TEST_CASE(name, tags)                                         \
     static void openPMD_parallel_##name();                                     \
     TEST_CASE(#name, tags)                                                     \
@@ -53,14 +63,6 @@
     }                                                                          \
     static void openPMD_parallel_##name()
 
-#if !openPMD_HAVE_MPI
-TEST_CASE("none", "[parallel]")
-{}
-
-#else
-
-#include <mpi.h>
-
 #if openPMD_HAVE_ADIOS2
 #include <adios2.h>
 #define HAS_ADIOS_2_8 (ADIOS2_VERSION_MAJOR * 100 + ADIOS2_VERSION_MINOR >= 208)