fix test_dashboard_port_zero test

distributed/cli/tests/test_dask_scheduler.py

@@ -4,6 +4,7 @@
 pytest.importorskip("requests")
 
 import os
+import re
 import shutil
 import sys
 import tempfile
@@ -21,6 +22,7 @@
 from distributed.metrics import time
 from distributed.utils import get_ip, get_ip_interface
 from distributed.utils_test import (
+    _TEST_TIMEOUT,
     assert_can_connect_from_everywhere_4_6,
     assert_can_connect_locally_4,
     popen,
@@ -218,13 +220,14 @@ def test_scheduler_port_zero(loop):
 def test_dashboard_port_zero(loop):
     pytest.importorskip("bokeh")
     with popen(["dask-scheduler", "--dashboard-address", ":0"]) as proc:
-        count = 0
-        while count < 1:
+        pattern = re.compile(r".*dashboard at:\s+:(\d)+$")
+        start = time()
+        while time() - start < _TEST_TIMEOUT:
             line = proc.stderr.readline()
-            if b"dashboard" in line.lower():
-                sleep(0.01)
-                count += 1
-                assert b":0" not in line
+            m = pattern.match(line.decode())
+            if m:
+                assert m.group(0) != "0"
+                return
 
 
 PRELOAD_TEXT = """