Test suite sporadically fails with test_asynchronous_queue.rb:44

[mattrayner]

Whilst working on #48 I've noticed that you have a sporadic test failure (appears roughly one in 10 times for me)

Stack trace

================================================================================================================================================
Error: test_flush_works_as_expected(TestAsynchronousQueue)
:
  fatal: No live threads left. Deadlock?
  1 threads, 1 sleeps current:0x00007ff7cd7b8930 main thread:0x00007ff7cbc0c4b0
  * #<Thread:0x00007ff7cc081c60 sleep_forever>
     rb_thread_t:0x00007ff7cbc0c4b0 native:0x00007fff928ab380 int:1
     /Users/mattrayner/projects/ApplicationInsights-Ruby/lib/application_insights/channel/event.rb:61:in `sleep'
     /Users/mattrayner/projects/ApplicationInsights-Ruby/lib/application_insights/channel/event.rb:61:in `wait'
     /Users/mattrayner/projects/ApplicationInsights-Ruby/lib/application_insights/channel/event.rb:61:in `block in wait'
     /Users/mattrayner/projects/ApplicationInsights-Ruby/lib/application_insights/channel/event.rb:60:in `synchronize'
     /Users/mattrayner/projects/ApplicationInsights-Ruby/lib/application_insights/channel/event.rb:60:in `wait'
     /Users/mattrayner/projects/ApplicationInsights-Ruby/test/application_insights/channel/test_asynchronous_queue.rb:44:in `test_flush_works_as_expected'
     /Users/mattrayner/.rvm/gems/ruby-2.5.1/gems/test-unit-3.0.9/lib/test/unit/testcase.rb:697:in `run_test'
     /Users/mattrayner/.rvm/gems/ruby-2.5.1/gems/test-unit-3.0.9/lib/test/unit/testcase.rb:437:in `run'
     /Users/mattrayner/.rvm/gems/ruby-2.5.1/gems/test-unit-3.0.9/lib/test/unit/testsuite.rb:121:in `run_test'
     /Users/mattrayner/.rvm/gems/ruby-2.5.1/gems/test-unit-3.0.9/lib/test/unit/testsuite.rb:53:in `run'
     /Users/mattrayner/.rvm/gems/ruby-2.5.1/gems/test-unit-3.0.9/lib/test/unit/testsuite.rb:121:in `run_test'
     /Users/mattrayner/.rvm/gems/ruby-2.5.1/gems/test-unit-3.0.9/lib/test/unit/testsuite.rb:53:in `run'
     /Users/mattrayner/.rvm/gems/ruby-2.5.1/gems/test-unit-3.0.9/lib/test/unit/ui/testrunnermediator.rb:65:in `run_suite'
     /Users/mattrayner/.rvm/gems/ruby-2.5.1/gems/test-unit-3.0.9/lib/test/unit/ui/testrunnermediator.rb:44:in `block in run'
     /Users/mattrayner/.rvm/gems/ruby-2.5.1/gems/test-unit-3.0.9/lib/test/unit/ui/testrunnermediator.rb:100:in `with_listener'
     /Users/mattrayner/.rvm/gems/ruby-2.5.1/gems/test-unit-3.0.9/lib/test/unit/ui/testrunnermediator.rb:40:in `run'
     /Users/mattrayner/.rvm/gems/ruby-2.5.1/gems/test-unit-3.0.9/lib/test/unit/ui/testrunner.rb:40:in `start_mediator'
     /Users/mattrayner/.rvm/gems/ruby-2.5.1/gems/test-unit-3.0.9/lib/test/unit/ui/testrunner.rb:25:in `start'
     /Users/mattrayner/.rvm/gems/ruby-2.5.1/gems/test-unit-3.0.9/lib/test/unit/ui/testrunnerutilities.rb:24:in `run'
     /Users/mattrayner/.rvm/gems/ruby-2.5.1/gems/test-unit-3.0.9/lib/test/unit/autorunner.rb:403:in `block in run'
     /Users/mattrayner/.rvm/gems/ruby-2.5.1/gems/test-unit-3.0.9/lib/test/unit/autorunner.rb:459:in `change_work_directory'
     /Users/mattrayner/.rvm/gems/ruby-2.5.1/gems/test-unit-3.0.9/lib/test/unit/autorunner.rb:402:in `run'
     /Users/mattrayner/.rvm/gems/ruby-2.5.1/gems/test-unit-3.0.9/lib/test/unit/autorunner.rb:59:in `run'
     /Users/mattrayner/.rvm/gems/ruby-2.5.1/gems/test-unit-3.0.9/lib/test/unit.rb:502:in `block (2 levels) in <top (required)>'
/Users/mattrayner/projects/ApplicationInsights-Ruby/lib/application_insights/channel/event.rb:61:in `sleep'
/Users/mattrayner/projects/ApplicationInsights-Ruby/lib/application_insights/channel/event.rb:61:in `wait'
/Users/mattrayner/projects/ApplicationInsights-Ruby/lib/application_insights/channel/event.rb:61:in `block in wait'
/Users/mattrayner/projects/ApplicationInsights-Ruby/lib/application_insights/channel/event.rb:60:in `synchronize'
/Users/mattrayner/projects/ApplicationInsights-Ruby/lib/application_insights/channel/event.rb:60:in `wait'
/Users/mattrayner/projects/ApplicationInsights-Ruby/test/application_insights/channel/test_asynchronous_queue.rb:44:in `test_flush_works_as_expected'
     41:     assert_equal false, result
     42:     queue.flush
     43:     assert_equal 1, sender.start_call_count
  => 44:     result = queue.flush_notification.wait
     45:     assert_equal true, result
     46:   end
     47: end
================================================================================================================================================

I'm going to have a go at investigating, but wanted to raise it early

[yantang-msft]

I experienced the same issue, this assertion is fairly unreliable.
To be more concrete, once the sender thread reaches to this line https://github.com/Microsoft/ApplicationInsights-Ruby/blob/develop/lib/application_insights/channel/asynchronous_sender.rb#L104
before the assertion, the notification will be clear, thus result = queue.flush_notification.wait will return false.
I've fixed this in #57, which simply drops this assertion. The main purpose of this test case is to make sure when flush is called, the sender will start().