avoid global namespace import in header, more consistency

unittest/formats/test_dump_cfg.cpp

@@ -23,6 +23,7 @@ using ::testing::Eq;
 
 bool verbose = false;
 
+namespace LAMMPS_NS {
 class DumpCfgTest : public MeltTest {
     std::string dump_style = "cfg";
 
@@ -143,6 +144,7 @@ TEST_F(DumpCfgTest, no_unwrap_no_buffer_run0)
     ASSERT_THAT(lines[0], Eq("Number of particles = 32"));
     delete_file("dump_cfg_no_unwrap_no_buffer_run0.melt.cfg");
 }
+}
 
 int main(int argc, char **argv)
 {
@@ -151,7 +153,7 @@ int main(int argc, char **argv)
 
     // handle arguments passed via environment variable
     if (const char *var = getenv("TEST_ARGS")) {
-        std::vector<std::string> env = utils::split_words(var);
+        std::vector<std::string> env = LAMMPS_NS::utils::split_words(var);
         for (auto arg : env) {
             if (arg == "-v") {
                 verbose = true;