diff --git a/src/testdir/commondumps.vim b/src/testdir/commondumps.vim
new file mode 100644
index 0000000..ed70280
--- /dev/null
+++ b/src/testdir/commondumps.vim
@@ -0,0 +1,76 @@
+vim9script
+
+# (Script-local.)
+#
+# Render a loaded screendump file or the difference of a loaded screendump
+# file and its namesake file from the "dumps" directory.
+def Render()
+  const failed_fname: string = bufname()
+  try
+    setlocal suffixesadd=.dump
+    const dumps_fname: string = findfile(
+			fnamemodify(failed_fname, ':p:t'),
+			fnamemodify(failed_fname, ':p:h:h') .. '/dumps')
+    if filereadable(dumps_fname)
+      term_dumpdiff(failed_fname, dumps_fname)
+    else
+      term_dumpload(failed_fname)
+    endif
+  finally
+    exec 'bwipeout ' .. failed_fname
+  endtry
+enddef
+
+# Search for the "failed" directory in the passed _subtreedirname_ directories
+# (usually "\<src\>" or "\<syntax\>") and, if found, select its passed _count_
+# occurence, add all its "*.dump" files to the argument list and list them;
+# also define a BufRead autocommand that would invoke "Render()" for every
+# "*.dump" file.
+def g:Init(subtreedirname: string, count: number)
+  # Support sourcing this script from any directory in the direct path that
+  # leads to the project's root directory.
+  const failed_path: string = finddir('failed', getcwd() .. '/**', -1)
+    ->filter(((cwdpath: string, parentdirname: string) =>
+			(_: number, dirpath: string) =>
+	cwdpath =~ parentdirname || dirpath =~ parentdirname)(
+			getcwd(),
+			subtreedirname))
+    ->get(count, '') .. '/'
+  var error: string = null_string
+
+  if failed_path == '/'
+    error = 'No such directory: "failed"'
+  else
+    const failed_fnames: string = failed_path .. readdir(failed_path,
+			(fname: string) => fname =~ '^.\+\.dump$')
+      ->join(' ' .. failed_path)
+
+    if failed_fnames =~ 'failed/$'
+      error = 'No such file: "*.dump"'
+    else
+      exec ':0argedit ' .. failed_fnames
+      buffers
+    endif
+  endif
+
+  autocmd_add([{
+    replace:	true,
+    group:	'viewdumps',
+    event:	'BufRead',
+    pattern:	'*.dump',
+    cmd:	'Render()',
+  }])
+
+  # Unconditionally help, in case a list of filenames is passed to the
+  # command, the first terminal window with its BufRead event.
+  silent doautocmd viewdumps BufRead
+
+  if error != null_string
+    # Instead of sleeping, fill half a window with blanks and prompt
+    # hit-enter.
+    echom error .. repeat("\x20",
+	(winwidth(0) * (winheight(0) / 2) - strlen(error)))
+  endif
+enddef
+
+# vim:fdm=syntax:sw=2:ts=8:noet:nolist:nosta: