@Override
    public int getNumberOfOutstandingRequests() {
        return requestsNotReturned.get();
    }
@Test
    void testAddAndHandleRequest() throws Exception {
        addRequest();
        assertThat(writer.getNumberOfOutstandingRequests())
                .withFailMessage("Didn't increment number of outstanding requests.")
                .isOne();

        handleRequest();
        assertThat(writer.getNumberOfOutstandingRequests())
                .withFailMessage("Didn't decrement number of outstanding requests.")
                .isZero();
    }