patch 8.2.0522: several errors are not tested for

Problem:    Several errors are not tested for.
Solution:   Add tests. (Yegappan Lakshmanan, closes #5892)

src/testdir/test_digraph.vim

@@ -210,6 +210,8 @@ func Test_digraphs()
   call Put_Dig("00")
   call Put_Dig("el")
   call assert_equal(['␀', 'ü', '∞', 'l'], getline(line('.')-3,line('.')))
+  call assert_fails('exe "digraph a\<Esc> 100"', 'E104:')
+  call assert_fails('exe "digraph \<Esc>a 100"', 'E104:')
   bw!
 endfunc
 
@@ -475,4 +477,15 @@ func Test_show_digraph_cp1251()
   bwipe!
 endfunc
 
+" Test for error in a keymap file
+func Test_loadkeymap_error()
+  if !has('keymap')
+    return
+  endif
+  call assert_fails('loadkeymap', 'E105:')
+  call writefile(['loadkeymap', 'a'], 'Xkeymap')
+  call assert_fails('source Xkeymap', 'E791:')
+  call delete('Xkeymap')
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab