Improve blockingWait test

Summary: Previously if the loop simply failed to execute the test could pass, add some minor changes to ensure control flow is as required.

Reviewed By: andriigrynenko

Differential Revision: D19960864

fbshipit-source-id: 5a437d9e7d3b7c249cbf999fe7ea5eecfe668658

folly/experimental/coro/test/BlockingWaitTest.cpp

@@ -274,17 +274,21 @@ struct ExpectedException {};
 TEST_F(BlockingWaitTest, WaitTaskInFiberException) {
   folly::EventBase evb;
   auto& fm = folly::fibers::getFiberManager(evb);
-  fm.addTask([] {
+  EXPECT_TRUE(
+      fm.addTaskFuture([&] {
           try {
             folly::coro::blockingWait(
                 folly::coro::co_invoke([&]() -> folly::coro::Task<void> {
-            folly::via(co_await folly::coro::co_current_executor, []() {});
+                  folly::via(
+                      co_await folly::coro::co_current_executor, []() {});
                   throw ExpectedException();
                 }));
+            return false;
           } catch (const ExpectedException&) {
+            return true;
           }
-  });
-  evb.loop();
+        })
+          .getVia(&evb));
 }
 
 TEST_F(BlockingWaitTest, WaitOnSemiFuture) {