--- a/tests/run-tests.py	Thu May 06 19:39:19 2021 -0400
+++ b/tests/run-tests.py	Wed May 19 17:19:46 2021 +0200
@@ -1386,6 +1386,8 @@
         env['PYTHONUSERBASE'] = sysconfig.get_config_var('userbase') or ''
         env['HGEMITWARNINGS'] = '1'
         env['TESTTMP'] = _bytes2sys(self._testtmp)
+        docket_id_file = os.path.join(_bytes2sys(self._testtmp), 'DOCKETID')
+        env['HGTEST_DOCKETIDFILE'] = docket_id_file
         env['TESTNAME'] = self.name
         env['HOME'] = _bytes2sys(self._testtmp)
         if os.name == 'nt':