vim-patch:8.2.1747: result of expand() unexpectedly depends on 'completeslash'

Problem:    Result of expand() unexpectedly depends on 'completeslash'.
Solution:   Temporarily reset 'completeslash'. (Yasuhiro Matsumoto,
            closes vim/vim#7021)
8f187fc630

src/nvim/testdir/test_ins_complete.vim

@@ -414,6 +414,19 @@ func Test_ins_completeslash()
   set completeslash=
 endfunc
 
+func Test_issue_7021()
+  CheckMSWindows
+
+  let orig_shellslash = &shellslash
+  set noshellslash
+
+  set completeslash=slash
+  call assert_false(expand('~') =~ '/')
+
+  let &shellslash = orig_shellslash
+  set completeslash=
+endfunc
+
 func Test_pum_with_folds_two_tabs()
   CheckScreendump