patch 8.2.0212: missing search/substitute pattern hardly tested

Problem:    Missing search/substitute pattern hardly tested.
Solution:   Add test_clear_search_pat() and tests. (Yegappan Lakshmanan,
            closes #5579)
diff --git a/src/testdir/test_search.vim b/src/testdir/test_search.vim
index 89ca6e1..69d0073 100644
--- a/src/testdir/test_search.vim
+++ b/src/testdir/test_search.vim
@@ -1455,3 +1455,44 @@
   set t_PE=
   exe "norm /\x80PS"
 endfunc
+
+" Test for command failures when the last search pattern is not set.
+func Test_search_with_no_last_pat()
+  call test_clear_search_pat()
+  call assert_fails("normal i\<C-R>/\e", 'E35:')
+  call assert_fails("exe '/'", 'E35:')
+  call assert_fails("exe '?'", 'E35:')
+  call assert_fails("/", 'E35:')
+  call assert_fails("?", 'E35:')
+  call assert_fails("normal n", 'E35:')
+  call assert_fails("normal N", 'E35:')
+  call assert_fails("normal gn", 'E35:')
+  call assert_fails("normal gN", 'E35:')
+  call assert_fails("normal cgn", 'E35:')
+  call assert_fails("normal cgN", 'E35:')
+  let p = []
+  let p = @/
+  call assert_equal('', p)
+  call assert_fails("normal :\<C-R>/", 'E35:')
+  call assert_fails("//p", 'E35:')
+  call assert_fails(";//p", 'E35:')
+  call assert_fails("??p", 'E35:')
+  call assert_fails(";??p", 'E35:')
+  call assert_fails('g//p', 'E476:')
+  call assert_fails('v//p', 'E476:')
+endfunc
+
+" Test for using tilde (~) atom in search. This should use the last used
+" substitute pattern
+func Test_search_tilde_pat()
+  call test_clear_search_pat()
+  set regexpengine=1
+  call assert_fails('exe "normal /~\<CR>"', 'E33:')
+  call assert_fails('exe "normal ?~\<CR>"', 'E33:')
+  set regexpengine=2
+  call assert_fails('exe "normal /~\<CR>"', 'E383:')
+  call assert_fails('exe "normal ?~\<CR>"', 'E383:')
+  set regexpengine&
+endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab