bufferpool2.0 tests: add read/write verification

Bug: 112203066
Bug: 113798958
Change-Id: I3969903c7263654bf1fecf012cf9185acd60ef58
diff --git a/media/bufferpool/2.0/tests/single.cpp b/media/bufferpool/2.0/tests/single.cpp
index 5c6d1c7..777edcf 100644
--- a/media/bufferpool/2.0/tests/single.cpp
+++ b/media/bufferpool/2.0/tests/single.cpp
@@ -147,11 +147,13 @@
 
   status = mManager->allocate(mConnectionId, vecParams, &allocHandle, &sbuffer);
   ASSERT_TRUE(status == ResultStatus::OK);
+  ASSERT_TRUE(TestBufferPoolAllocator::Fill(allocHandle, 0x77));
   status = mManager->postSend(mReceiverId, sbuffer, &transactionId, &postUs);
   ASSERT_TRUE(status == ResultStatus::OK);
   status = mManager->receive(mReceiverId, transactionId, sbuffer->mId, postUs,
                              &recvHandle, &rbuffer);
   EXPECT_TRUE(status == ResultStatus::OK);
+  ASSERT_TRUE(TestBufferPoolAllocator::Verify(recvHandle, 0x77));
 }
 
 }  // anonymous namespace