Adding comment in unit test for readability

Signed-off-by: Sagar Upadhyaya <sagar.upadhyaya.121@gmail.com>

modules/cache-common/src/test/java/org/opensearch/cache/common/tier/TieredSpilloverCacheTests.java

@@ -154,6 +154,7 @@ public void testComputeIfAbsentWithFactoryBasedCacheCreation() throws Exception
         }
         // Verify on heap cache size.
         assertEquals(onHeapCacheSize, tieredSpilloverCache.getOnHeapCache().count());
+        // Verify disk cache size.
         assertEquals(numOfItems1 - onHeapCacheSize, tieredSpilloverCache.getDiskCache().count());
     }