Improve error message of flushWithNullOutputStream test

Author: philsttr

src/test/java/net/logstash/logback/appender/DelegatingAsyncDisruptorAppenderTest.java

@@ -215,7 +215,8 @@ public void flushWithNullOutputStream() {
         outputStreamDelegate.setOutputStream(null);
         appender.doAppend(event);
 
-        assertThat(appender.getStatusManager().getCount()).isZero();
+        // Test the status list, rather than getCount(), so a helpful error message is generated if the list is not empty
+        assertThat(appender.getStatusManager().getCopyOfStatusList()).isEmpty();
     }