Some of the unit-tests for SharedFuture (e.g., ConcurrentTest_ManySharedFutures) create a number of worker threads to test the behavior of futures in presence of concurrency. An attempt to delete these threads before they are joined (e.g., due to an exception) would cause the termination of the unit-test process (i.e., invocation of std::terminate).

To prevent the termination and ensure the real cause of failure remains always visible, we must ensure all worker threads are joined before they go out-of-scope.