add test

test/system/test_os.f90

@@ -1,6 +1,6 @@
 module test_os
  use testdrive, only : new_unittest, unittest_type, error_type, check, skip_test
- use stdlib_system, only: get_runtime_os, OS_WINDOWS, OS_UNKNOWN, OS_TYPE, is_windows
+ use stdlib_system, only: get_runtime_os, OS_WINDOWS, OS_UNKNOWN, OS_TYPE, is_windows, null_device
 
  implicit none
 
@@ -13,7 +13,8 @@ subroutine collect_suite(testsuite)
 
  testsuite = [ &
  new_unittest('test_get_runtime_os', test_get_runtime_os), &
- new_unittest('test_is_windows', test_is_windows) &
+ new_unittest('test_is_windows', test_is_windows), &
+ new_unittest('test_null_device', test_null_device) &
  ]
  end subroutine collect_suite
 
@@ -38,6 +39,26 @@ subroutine test_is_windows(error)
 
  end subroutine test_is_windows
 
+ !> Test that the null_device is valid by writing something to it
+ subroutine test_null_device(error)
+ type(error_type), allocatable, intent(out) :: error
+ integer :: unit, ios
+ character(len=512) :: iomsg
+
+ ! Try opening the null device for writing
+ open(newunit=unit, file=null_device(), status='old', action='write', iostat=ios, iomsg=iomsg) 
+ call check(error, ios==0, 'Cannot open null_device unit: '//trim(iomsg))
+ if (allocated(error)) return
+
+ write(unit, *, iostat=ios, iomsg=iomsg) 'Hello, World!' 
+ call check(error, ios==0, 'Cannot write to null_device unit: '//trim(iomsg))
+ if (allocated(error)) return 
+
+ close(unit, iostat=ios, iomsg=iomsg)
+ call check(error, ios==0, 'Cannot close null_device unit: '//trim(iomsg))
+ if (allocated(error)) return 
+
+ end subroutine test_null_device
 
 end module test_os