Fix invalid path write attempt test

Actually since Gitlab CI is running as root, one must use ioctl to
make directory immutable. Otherwise, root can create the file which
invalidates the test.

tests/test_OFStream.cpp

@@ -7,6 +7,12 @@
 
 #include <filesystem>
 
+#ifdef __linux__
+#include <fcntl.h>
+#include <linux/fs.h>
+#include <sys/ioctl.h>
+#endif   // __linux__
+
 // clazy:excludeall=non-pod-global-static
 
 TEST_CASE("OFStream", "[language]")
@@ -49,6 +55,7 @@ TEST_CASE("OFStream", "[language]")
     REQUIRE(not std::filesystem::exists(filename));
   }
 
+#ifdef __linux__
   SECTION("invalid filename")
   {
     if (parallel::rank() == 0) {
@@ -60,8 +67,14 @@ TEST_CASE("OFStream", "[language]")
                                      std::filesystem::perms::others_all,
                                    std::filesystem::perm_options::remove);
 
+      int fd    = open("tests/badpath/invalidpath", O_DIRECTORY);
+      int flags = FS_IMMUTABLE_FL;
+      ioctl(fd, FS_IOC_SETFLAGS, &flags);
       REQUIRE_THROWS_WITH(std::make_shared<OFStream>(filename), "error: cannot create file " + filename);
 
+      flags = 0;
+      ioctl(fd, FS_IOC_SETFLAGS, &flags);
+
       std::filesystem::permissions(directory,
                                    std::filesystem::perms::owner_all | std::filesystem::perms::group_all |
                                      std::filesystem::perms::others_all,
@@ -69,4 +82,5 @@ TEST_CASE("OFStream", "[language]")
       std::filesystem::remove_all("tests/badpath");
     }
   }
+#endif   // __linux__
 }