对于此场景，请改用集成测试。
在下面的代码中，行 env.execute(); 将运行管道并序列化运算符 MultiplyByTwo 以及 CollectSink .
你可以用同样的方法来测试 RichFlatMapFunction 是可序列化的。

public class ExampleIntegrationTest extends AbstractTestBase {

    @Test
    public void testMultiply() throws Exception {
        StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();

        // configure your test environment
        env.setParallelism(1);

        // values are collected in a static variable
        CollectSink.values.clear();

        // create a stream of custom elements and apply transformations
        env.fromElements(1L, 21L, 22L)
                .map(new MultiplyByTwo())
                .addSink(new CollectSink());

        // execute
        env.execute();

        // verify your results
        assertEquals(Lists.newArrayList(2L, 42L, 44L), CollectSink.values);
    }

    // create a testing sink
    private static class CollectSink implements SinkFunction<Long> {

        // must be static
        public static final List<Long> values = new ArrayList<>();

        @Override
        public synchronized void invoke(Long value) throws Exception {
            values.add(value);
        }
    }
}

参考文献：https://ci.apache.org/projects/flink/flink-docs-stable/dev/stream/testing.html#integration-测试