patch 8.2.0531: various errors not tested

Problem:    Various errors not tested.
Solution:   Add tests. (Yegappan Lakshmanan, closes #5895)
diff --git a/src/testdir/test_source.vim b/src/testdir/test_source.vim
index ba6fd5a..b22e57c 100644
--- a/src/testdir/test_source.vim
+++ b/src/testdir/test_source.vim
@@ -87,4 +87,10 @@
   call delete('Xscript.vim')
 endfunc
 
+func Test_source_error()
+  call assert_fails('scriptencoding utf-8', 'E167:')
+  call assert_fails('finish', 'E168:')
+  call assert_fails('scriptversion 2', 'E984:')
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab