Loosen the guarantees of this test

This test hits the race condition described in `onClose` a little less
than once in a thousand runs on my machine, so we can't check for the
same level of strict internal consistency between the two data
structures (it's possible for the cache to contain a bitset that isn't
referenced by the keysByIndex structure, and that's okay).

Author: joegallo

x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/security/authz/accesscontrol/DocumentSubsetBitsetCacheTests.java

@@ -314,12 +314,12 @@ public void testCacheUnderConcurrentAccess() throws Exception {
             .put(DocumentSubsetBitsetCache.CACHE_SIZE_SETTING.getKey(), maxCacheBytes + "b")
             .build();
 
+        final DocumentSubsetBitsetCache cache = new DocumentSubsetBitsetCache(settings);
+        assertThat(cache.entryCount(), equalTo(0));
+        assertThat(cache.ramBytesUsed(), equalTo(0L));
+
         final ExecutorService threads = Executors.newFixedThreadPool(concurrentThreads + 1);
         try {
-            final DocumentSubsetBitsetCache cache = new DocumentSubsetBitsetCache(settings);
-            assertThat(cache.entryCount(), equalTo(0));
-            assertThat(cache.ramBytesUsed(), equalTo(0L));
-
             runTestOnIndices(numberOfIndices, contexts -> {
                 final CountDownLatch start = new CountDownLatch(concurrentThreads);
                 final CountDownLatch end = new CountDownLatch(concurrentThreads);
@@ -360,7 +360,7 @@ public void testCacheUnderConcurrentAccess() throws Exception {
 
                 threads.shutdown();
                 assertTrue("Cleanup thread did not complete in expected time", threads.awaitTermination(3, TimeUnit.SECONDS));
-                cache.verifyInternalConsistency();
+                cache.verifyInternalConsistencyKeysToCache();
 
                 // Due to cache evictions, we must get more bitsets than fields
                 assertThat(uniqueBitSets.size(), greaterThan(FIELD_COUNT));
@@ -373,6 +373,8 @@ public void testCacheUnderConcurrentAccess() throws Exception {
         } finally {
             threads.shutdown();
         }
+
+        cache.verifyInternalConsistencyKeysToCache();
     }
 
     @AwaitsFix(bugUrl = "todo")