patch 8.2.2901: some operators not fully tested

Problem:    Some operators not fully tested.
Solution:   Add a few test cases. (Yegappan Lakshmanan, closes #8282)
diff --git a/src/testdir/test_increment.vim b/src/testdir/test_increment.vim
index 1a631ec..beacb0a 100644
--- a/src/testdir/test_increment.vim
+++ b/src/testdir/test_increment.vim
@@ -876,4 +876,21 @@
   set virtualedit&
 endfunc
 
+" Test for incrementing a signed hexadecimal and octal number
+func Test_normal_increment_signed_hexoct_nr()
+  new
+  " negative sign before a hex number should be ignored
+  call setline(1, ["-0x9"])
+  exe "norm \<C-A>"
+  call assert_equal(["-0xa"], getline(1, '$'))
+  exe "norm \<C-X>"
+  call assert_equal(["-0x9"], getline(1, '$'))
+  call setline(1, ["-007"])
+  exe "norm \<C-A>"
+  call assert_equal(["-010"], getline(1, '$'))
+  exe "norm \<C-X>"
+  call assert_equal(["-007"], getline(1, '$'))
+  bw!
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab