patch 8.2.2592: code coverage could be improved

Problem:    Code coverage could be improved.
Solution:   Add a few more tests. (Dominique Pellé, closes #7957)
diff --git a/src/testdir/test_textformat.vim b/src/testdir/test_textformat.vim
index eac1c19..32ff3cc 100644
--- a/src/testdir/test_textformat.vim
+++ b/src/testdir/test_textformat.vim
@@ -858,6 +858,21 @@
   close!
 endfunc
 
+func Test_mps_error()
+  let encoding_save = &encoding
+
+  for e in ['utf-8', 'latin1']
+    exe 'set encoding=' .. e
+
+    call assert_fails('set mps=<:', 'E474:', e)
+    call assert_fails('set mps=:>', 'E474:', e)
+    call assert_fails('set mps=<>', 'E474:', e)
+    call assert_fails('set mps=<:>_', 'E474:', e)
+  endfor
+
+  let &encoding = encoding_save
+endfunc
+
 " Test for ra on multi-byte characters
 func Test_ra_multibyte()
   new