diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index 9b5d976..b25d988 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -1497,6 +1497,13 @@
   call assert_equal("a", trim("a", ""))
   call assert_equal("", trim("", "a"))
 
+  call assert_equal("vim", trim("  vim  ", " ", 0))
+  call assert_equal("vim  ", trim("  vim  ", " ", 1))
+  call assert_equal("  vim", trim("  vim  ", " ", 2))
+  call assert_fails('eval trim("  vim  ", " ", [])', 'E745:')
+  call assert_fails('eval trim("  vim  ", " ", -1)', 'E475:')
+  call assert_fails('eval trim("  vim  ", " ", 3)', 'E475:')
+
   let chars = join(map(range(1, 0x20) + [0xa0], {n -> n->nr2char()}), '')
   call assert_equal("x", trim(chars . "x" . chars))