Avoid raising debuggee not finished error if assertions failed

When assertions failed, we should let the AssertionFailedError surface
and not calling flunk so we can get correct failure messages.

Author: st0012

test/support/protocol_test_case.rb

@@ -334,9 +334,12 @@ def execute_dap_scenario scenario
 
       attach_to_dap_server
       scenario.call
+    rescue Test::Unit::AssertionFailedError => e
+      is_assertion_failure = true
+      raise e
     ensure
       kill_remote_debuggee test_info
-      if name = test_info.failed_process
+      if name = test_info.failed_process && !is_assertion_failure
         flunk create_protocol_message "Expected the debuggee program to finish"
       end
       # Because the debuggee may be terminated by executing the following operations, we need to run them after `kill_remote_debuggee` method.