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 #7021)
diff --git a/src/testdir/test_ins_complete.vim b/src/testdir/test_ins_complete.vim
index 992fefa..f77512a 100644
--- a/src/testdir/test_ins_complete.vim
+++ b/src/testdir/test_ins_complete.vim
@@ -363,12 +363,12 @@
 " Test for insert path completion with completeslash option
 func Test_ins_completeslash()
   CheckMSWindows
-  
+
   call mkdir('Xdir')
   let orig_shellslash = &shellslash
   set cpt&
   new
-  
+
   set noshellslash
 
   set completeslash=
@@ -654,4 +654,17 @@
   close!
 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
+
 " vim: shiftwidth=2 sts=2 expandtab