new file mode 100644
--- /dev/null
+++ b/src/testdir/screendump.vim
@@ -0,0 +1,65 @@
+" Functions shared by tests making screen dumps.
+
+" Only load this script once.
+if exists('*RunVimInTerminal')
+  finish
+endif
+
+source shared.vim
+
+" Run Vim with "arguments" in a new terminal window.
+" By default uses a size of 20 lines and 75 columns.
+" Returns the buffer number of the terminal.
+"
+" Options is a dictionary (not used yet).
+func RunVimInTerminal(arguments, options)
+  " Make a horizontal and vertical split, so that we can get exactly the right
+  " size terminal window.  Works only when we currently have one window.
+  call assert_equal(1, winnr('$'))
+  split
+  vsplit
+
+  " Always doo this with 256 colors and a light background.
+  set t_Co=256
+  hi Normal ctermfg=0 ctermbg=15
+
+  let cmd = GetVimCommandClean()
+  let cmd .= ' ' . a:arguments
+  let buf = term_start(cmd, {'curwin': 1, 'term_rows': 20, 'term_cols': 75})
+  call assert_equal([20, 75], term_getsize(buf))
+
+  return buf
+endfunc
+
+" Stop a Vim running in terminal buffer "buf".
+func StopVimInTerminal(buf)
+  call assert_equal("running", term_getstatus(a:buf))
+  call term_sendkeys(a:buf, ":qa!\<cr>")
+  call WaitFor('term_getstatus(' . a:buf . ') == "finished"')
+  only!
+endfunc
+
+" Verify that Vim running in terminal buffer "buf" matches the screen dump.
+" The file name used is "dumps/{filename}.dump".
+" Will wait for up to a second for the screen dump to match.
+func VerifyScreenDump(buf, filename)
+  let reference = 'dumps/' . a:filename . '.dump'
+  let testfile = a:filename . '.dump.failed'
+
+  let i = 0
+  while 1
+    call delete(testfile)
+    call term_dumpwrite(a:buf, testfile)
+    if readfile(reference) == readfile(testfile)
+      call delete(testfile)
+      break
+    endif
+    if i == 100
+      " Leave the test file around for inspection.
+      call assert_report('See dump file difference: call term_dumpdiff("' . testfile . '", "' . reference . '")')
+      break
+    endif
+    sleep 10m
+    let i += 1
+  endwhile
+endfunc