patch 8.0.0351: no test for concatenating an empty string commit https://github.com/vim/vim/commit/218426896cbb2129aa4e85803ea97c5b57df1eaa Author: Bram Moolenaar <Bram@vim.org> Date: Thu Feb 23 13:50:38 2017 +0100 patch 8.0.0351: no test for concatenating an empty string Problem: No test for concatenating an empty string that results from out of bounds indexing. Solution: Add a simple test.

--- a/src/testdir/test_expr.vim
+++ b/src/testdir/test_expr.vim
@@ -473,3 +473,8 @@ func Test_setmatches()
   call setmatches(set)
   call assert_equal(exp, getmatches())
 endfunc
+
+func Test_empty_concatenate()
+  call assert_equal('b', 'a'[4:0] . 'b')
+  call assert_equal('b', 'b' . 'a'[4:0])
+endfunc