message: c-bindings: add a test for adios2_variable_name()
  which mostly goes to show that this is evil to use correctly.
diff: #endif
  #include <gtest/gtest.h>
  +#include <cstring>
  #include "SmallTestData_c.h"
  @@ -114,6 +115,14 @@ TEST_F(BPWriteTypesCC, ADIOS2BPWriteTypes)
  adios2_variable *varR32 = adios2_inquire_variable(ioH, "varR32");
  adios2_variable *varR64 = adios2_inquire_variable(ioH, "varR64");
  +
  + size_t size;
  + adios2_variable_name(NULL, &size, varStr);
  + char var_name[size + 1];
  + adios2_variable_name(var_name, &size, varStr);
  + var_name[size] = '\0';
  + EXPECT_EQ(strcmp(var_name, "varStr"), 0);
  +
  adios2_engine *engineH =
  adios2_open(ioH, "ctypes.bp", adios2_mode_write);
  