Test for log_heartbeat fails in timezones with non-integer offsets
The test for log_heartbeat contains the check
/* format_local_iso_time uses local tz, just check mins and secs. */ tt_ptr_op(strstr(va_arg(ap, char *), ":01:00"), OP_NE, NULL); /* end_buf */
which assumes that the timezone will only affect the hours. In timezones with half-hour or 15 minute offsets this test will always (incorrectly) fail.
I have a fix at https://github.com/fergus-dall/tor/tree/log_heartbeat_test which calls format_local_iso_time to figure out what to compare against.