patch 8.2.1505: not all file read and writecode is tested

Problem:    Not all file read and writecode is tested.
Solution:   Add a few tests. (Dominique Pellé, closes #6764)
diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index c2d9066..dc06bd7 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -2516,6 +2516,19 @@
 func Test_glob()
   call assert_equal('', glob(test_null_string()))
   call assert_equal('', globpath(test_null_string(), test_null_string()))
+
+  call writefile([], 'Xglob1')
+  call writefile([], 'XGLOB2')
+  set wildignorecase
+  " Sort output of glob() otherwise we end up with different
+  " ordering depending on whether file system is case-sensitive.
+  call assert_equal(['XGLOB2', 'Xglob1'], sort(glob('Xglob[12]', 0, 1)))
+  set wildignorecase&
+
+  call delete('Xglob1')
+  call delete('XGLOB2')
+
+  call assert_fails("call glob('*', 0, {})", 'E728:')
 endfunc
 
 " Test for browse()