diff --git a/src/testdir/test_functions.vim b/src/testdir/test_functions.vim
index ffc3bc3..49e5d1f 100644
--- a/src/testdir/test_functions.vim
+++ b/src/testdir/test_functions.vim
@@ -876,3 +876,26 @@
 
   let &shell = save_shell
 endfunc
+
+func Test_trim()
+  call assert_equal("Testing", trim("  \t\r\r\x0BTesting  \t\n\r\n\t\x0B\x0B"))
+  call assert_equal("Testing", trim("  \t  \r\r\n\n\x0BTesting  \t\n\r\n\t\x0B\x0B"))
+  call assert_equal("RESERVE", trim("xyz \twwRESERVEzyww \t\t", " wxyz\t"))
+  call assert_equal("wRE    \tSERVEzyww", trim("wRE    \tSERVEzyww"))
+  call assert_equal("abcd\t     xxxx   tail", trim(" \tabcd\t     xxxx   tail"))
+  call assert_equal("\tabcd\t     xxxx   tail", trim(" \tabcd\t     xxxx   tail", " "))
+  call assert_equal(" \tabcd\t     xxxx   tail", trim(" \tabcd\t     xxxx   tail", "abx"))
+  call assert_equal("RESERVE", trim("你RESERVE好", "你好"))
+  call assert_equal("您R E SER V E早", trim("你好您R E SER V E早好你你", "你好"))
+  call assert_equal("你好您R E SER V E早好你你", trim(" \n\r\r   你好您R E SER V E早好你你    \t  \x0B", ))
+  call assert_equal("您R E SER V E早好你你    \t  \x0B", trim("    你好您R E SER V E早好你你    \t  \x0B", " 你好"))
+  call assert_equal("您R E SER V E早好你你    \t  \x0B", trim("    tteesstttt你好您R E SER V E早好你你    \t  \x0B ttestt", " 你好tes"))
+  call assert_equal("您R E SER V E早好你你    \t  \x0B", trim("    tteesstttt你好您R E SER V E早好你你    \t  \x0B ttestt", "   你你你好好好tttsses"))
+  call assert_equal("留下", trim("这些些不要这些留下这些", "这些不要"))
+  call assert_equal("", trim("", ""))
+  call assert_equal("a", trim("a", ""))
+  call assert_equal("", trim("", "a"))
+
+  let chars = join(map(range(1, 0x20) + [0xa0], {n -> nr2char(n)}), '')
+  call assert_equal("x", trim(chars . "x" . chars))
+endfunc