add tolerance

Author: Fabien Coelho

test.py

@@ -684,8 +684,8 @@ def run():
     assert len(cache) == 32
     # 16 * 2 gets-no-hit + 16 * (nthreads - 1) get-with-hit
     hits = (nthreads - 1) / (nthreads + 1)
-    # FIXME the hit ratio may not be deterministic?
-    assert abs(cache.hits() - hits) < 0.01
+    # NOTE hit ratio is not deterministic
+    assert 0.75 * hits < cache.hits() <= hits
 
 def test_threads():
     cache = ctu.LockedCache(ctu.StatsCache(ctu.DictCache()), threading.RLock())