@AfterEach
    void cleanup() {
        executorService.shutdownNow();
    }
A suite of acceptance tests for compliance with RFC5861, which
describes the stale-if-error and stale-while-revalidate
Cache-Control extensions.
httpclient5-cache/src/test/java/org/apache/hc/client5/http/impl/cache/TestRFC5861Compliance.java