Loosen flaky test_timer which tends to fail on overloaded CI systems

Author: oremanj

.github/workflows/ci.yml

@@ -51,9 +51,11 @@ jobs:
           - python: '3.8'
             check_docs: '1'
             extra_name: ', check docs'
-          - python: '3.7'  # <- not actually used
-            pypy_nightly_branch: 'py3.7'
-            extra_name: ', pypy 3.7 nightly'
+        # pypy3.7-nightly produces an "OSError: handle is closed" in the
+        # bowels of multiprocessing after all tests appear to complete successfully
+        #  - python: '3.7'  # <- not actually used
+        #    pypy_nightly_branch: 'py3.7'
+        #    extra_name: ', pypy 3.7 nightly'
     steps:
       - name: Checkout
         uses: actions/checkout@v2

tests/aiotest/test_timer.py

@@ -24,7 +24,11 @@ def display_date(end_time, loop):
         loop.call_soon(display_date, [], loop)
         await h.wait()
 
-        assert len(result) == count, result
+        assert 2 <= len(result) <= 3
+        assert all(
+            later - earlier >= datetime.timedelta(microseconds=150000)
+            for earlier, later in zip(result[:-1], result[1:])
+        )
 
     @pytest.mark.trio
     async def test_later_stop_later(self, loop):