patch 8.2.0522: several errors are not tested for

Problem:    Several errors are not tested for.
Solution:   Add tests. (Yegappan Lakshmanan, closes #5892)
diff --git a/src/testdir/test_viminfo.vim b/src/testdir/test_viminfo.vim
index 044da0a..b4708f5 100644
--- a/src/testdir/test_viminfo.vim
+++ b/src/testdir/test_viminfo.vim
@@ -815,3 +815,24 @@
   call test_settime(0)
   let &viminfo=save_viminfo
 endfunc
+
+" Test for errors in setting 'viminfo'
+func Test_viminfo_option_error()
+  " Missing number
+  call assert_fails('set viminfo=\"', 'E526:')
+  for c in split("'/:<@s", '\zs')
+    call assert_fails('set viminfo=' .. c, 'E526:')
+  endfor
+
+  " Missing comma
+  call assert_fails('set viminfo=%10!', 'E527:')
+  call assert_fails('set viminfo=!%10', 'E527:')
+  call assert_fails('set viminfo=h%10', 'E527:')
+  call assert_fails('set viminfo=c%10', 'E527:')
+  call assert_fails('set viminfo=:10%10', 'E527:')
+
+  " Missing ' setting
+  call assert_fails('set viminfo=%10', 'E528:')
+endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab