question: public static void assertThrowsCompletionException ( final Consumer < Void > consumer , final Class < ? > exceptionClass ) { try { consumer . accept ( null ) ; } catch ( final CompletionException completionEx ) { final Throwable ex = completionEx . getCause ( ) ; if ( ex . getClass ( ) == exceptionClass ) { return ; } Assert . fail ( String . format ( "unexpected exception of type %s was thrown" , ex . getClass ( ) ) ) ; } Assert . fail ( String . format ( "expected exception of type %s was not thrown" , exceptionClass ) ) ; }
target:  Asserts that the execution of consumer throws a completion exception wrapping an exception of the specific class.