测试 #

测试是每个软件开发过程中不可或缺的一部分， Apache Flink 同样提供了在测试金字塔的多个级别上测试应用程序代码的工具。

测试用户自定义函数 #

通常，我们可以假设 Flink 在用户自定义函数之外产生了正确的结果。因此，建议尽可能多的用单元测试来测试那些包含主要业务逻辑的类。

单元测试无状态、无时间限制的 UDF #

例如，让我们以以下无状态的 MapFunction 为例。

Java

public class IncrementMapFunction implements MapFunction<Long, Long> {

    @Override
    public Long map(Long record) throws Exception {
        return record + 1;
    }
}

Scala

class IncrementMapFunction extends MapFunction[Long, Long] {

    override def map(record: Long): Long = {
        record + 1
    }
}

通过传递合适地参数并验证输出，你可以很容易的使用你喜欢的测试框架对这样的函数进行单元测试。

Java

public class IncrementMapFunctionTest {

    @Test
    public void testIncrement() throws Exception {
        // instantiate your function
        IncrementMapFunction incrementer = new IncrementMapFunction();

        // call the methods that you have implemented
        assertEquals(3L, incrementer.map(2L));
    }
}

Scala

class IncrementMapFunctionTest extends FlatSpec with Matchers {

    "IncrementMapFunction" should "increment values" in {
        // instantiate your function
        val incrementer: IncrementMapFunction = new IncrementMapFunction()

        // call the methods that you have implemented
        incremeter.map(2) should be (3)
    }
}

类似地，对于使用 org.apache.flink.util.Collector 的用户自定义函数（例如FlatMapFunction 或者 ProcessFunction），可以通过提供模拟对象而不是真正的 collector 来轻松测试。具有与 IncrementMapFunction 相同功能的 FlatMapFunction 可以按照以下方式进行单元测试。

Java

public class IncrementFlatMapFunctionTest {

    @Test
    public void testIncrement() throws Exception {
        // instantiate your function
        IncrementFlatMapFunction incrementer = new IncrementFlatMapFunction();

        Collector<Integer> collector = mock(Collector.class);

        // call the methods that you have implemented
        incrementer.flatMap(2L, collector);

        //verify collector was called with the right output
        Mockito.verify(collector, times(1)).collect(3L);
    }
}

Scala

class IncrementFlatMapFunctionTest extends FlatSpec with MockFactory {

    "IncrementFlatMapFunction" should "increment values" in {
       // instantiate your function
      val incrementer : IncrementFlatMapFunction = new IncrementFlatMapFunction()

      val collector = mock[Collector[Integer]]

      //verify collector was called with the right output
      (collector.collect _).expects(3)

      // call the methods that you have implemented
      flattenFunction.flatMap(2, collector)
  }
}

对有状态或及时 UDF 和自定义算子进行单元测试 #

对使用管理状态或定时器的用户自定义函数的功能测试会更加困难，因为它涉及到测试用户代码和 Flink 运行时的交互。为此，Flink 提供了一组所谓的测试工具，可用于测试用户自定义函数和自定义算子：

OneInputStreamOperatorTestHarness (适用于 DataStream 上的算子)
KeyedOneInputStreamOperatorTestHarness (适用于 KeyedStream 上的算子)
TwoInputStreamOperatorTestHarness (f适用于两个 DataStream 的 ConnectedStreams 算子)
KeyedTwoInputStreamOperatorTestHarness (适用于两个 KeyedStream 上的 ConnectedStreams 算子)

要使用测试工具，还需要一组其他的依赖项，请查阅配置小节了解更多细节。

现在，可以使用测试工具将记录和 watermark 推送到用户自定义函数或自定义算子中，控制处理时间，最后对算子的输出（包括旁路输出）进行校验。

Java


public class StatefulFlatMapTest {
    private OneInputStreamOperatorTestHarness<Long, Long> testHarness;
    private StatefulFlatMap statefulFlatMapFunction;

    @Before
    public void setupTestHarness() throws Exception {

        //instantiate user-defined function
        statefulFlatMapFunction = new StatefulFlatMapFunction();

        // wrap user defined function into a the corresponding operator
        testHarness = new OneInputStreamOperatorTestHarness<>(new StreamFlatMap<>(statefulFlatMapFunction));

        // optionally configured the execution environment
        testHarness.getExecutionConfig().setAutoWatermarkInterval(50);

        // open the test harness (will also call open() on RichFunctions)
        testHarness.open();
    }

    @Test
    public void testingStatefulFlatMapFunction() throws Exception {

        //push (timestamped) elements into the operator (and hence user defined function)
        testHarness.processElement(2L, 100L);

        //trigger event time timers by advancing the event time of the operator with a watermark
        testHarness.processWatermark(100L);

        //trigger processing time timers by advancing the processing time of the operator directly
        testHarness.setProcessingTime(100L);

        //retrieve list of emitted records for assertions
        assertThat(testHarness.getOutput(), containsInExactlyThisOrder(3L));

        //retrieve list of records emitted to a specific side output for assertions (ProcessFunction only)
        //assertThat(testHarness.getSideOutput(new OutputTag<>("invalidRecords")), hasSize(0))
    }
}

Scala

class StatefulFlatMapFunctionTest extends FlatSpec with Matchers with BeforeAndAfter {

  private var testHarness: OneInputStreamOperatorTestHarness[Long, Long] = null
  private var statefulFlatMap: StatefulFlatMapFunction = null

  before {
    //instantiate user-defined function
    statefulFlatMap = new StatefulFlatMap

    // wrap user defined function into a the corresponding operator
    testHarness = new OneInputStreamOperatorTestHarness[Long, Long](new StreamFlatMap(statefulFlatMap))

    // optionally configured the execution environment
    testHarness.getExecutionConfig().setAutoWatermarkInterval(50)

    // open the test harness (will also call open() on RichFunctions)
    testHarness.open()
  }

  "StatefulFlatMap" should "do some fancy stuff with timers and state" in {


    //push (timestamped) elements into the operator (and hence user defined function)
    testHarness.processElement(2, 100)

    //trigger event time timers by advancing the event time of the operator with a watermark
    testHarness.processWatermark(100)

    //trigger proccesign time timers by advancing the processing time of the operator directly
    testHarness.setProcessingTime(100)

    //retrieve list of emitted records for assertions
    testHarness.getOutput should contain (3)

    //retrieve list of records emitted to a specific side output for assertions (ProcessFunction only)
    //testHarness.getSideOutput(new OutputTag[Int]("invalidRecords")) should have size 0
  }
}

KeyedOneInputStreamOperatorTestHarness 和 KeyedTwoInputStreamOperatorTestHarness 可以通过为键的类另外提供一个包含 TypeInformation 的 KeySelector 来实例化。

Java


public class StatefulFlatMapFunctionTest {
    private OneInputStreamOperatorTestHarness<String, Long, Long> testHarness;
    private StatefulFlatMap statefulFlatMapFunction;

    @Before
    public void setupTestHarness() throws Exception {

        //instantiate user-defined function
        statefulFlatMapFunction = new StatefulFlatMapFunction();

        // wrap user defined function into a the corresponding operator
        testHarness = new KeyedOneInputStreamOperatorTestHarness<>(new StreamFlatMap<>(statefulFlatMapFunction), new MyStringKeySelector(), Types.STRING);

        // open the test harness (will also call open() on RichFunctions)
        testHarness.open();
    }

    //tests

}

Scala

class StatefulFlatMapTest extends FlatSpec with Matchers with BeforeAndAfter {

  private var testHarness: OneInputStreamOperatorTestHarness[String, Long, Long] = null
  private var statefulFlatMapFunction: FlattenFunction = null

  before {
    //instantiate user-defined function
    statefulFlatMapFunction = new StateFulFlatMap

    // wrap user defined function into a the corresponding operator
    testHarness = new KeyedOneInputStreamOperatorTestHarness(new StreamFlatMap(statefulFlatMapFunction),new MyStringKeySelector(), Types.STRING())

    // open the test harness (will also call open() on RichFunctions)
    testHarness.open()
  }

  //tests

}

在 Flink 代码库里可以找到更多使用这些测试工具的示例，例如：

org.apache.flink.streaming.runtime.operators.windowing.WindowOperatorTest 是测试算子和用户自定义函数（取决于处理时间和事件时间）的一个很好的例子。

注意 AbstractStreamOperatorTestHarness 及其派生类目前不属于公共 API，可以进行更改。

单元测试 Process Function #

考虑到它的重要性，除了之前可以直接用于测试 ProcessFunction 的测试工具之外，Flink 还提供了一个名为 ProcessFunctionTestHarnesses 的测试工具工厂类，可以简化测试工具的实例化。考虑以下示例：

注意要使用此测试工具，还需要引入上一节中介绍的依赖项。

Java

public static class PassThroughProcessFunction extends ProcessFunction<Integer, Integer> {

	@Override
	public void processElement(Integer value, Context ctx, Collector<Integer> out) throws Exception {
        out.collect(value);
	}
}

Scala

class PassThroughProcessFunction extends ProcessFunction[Integer, Integer] {

    @throws[Exception]
    override def processElement(value: Integer, ctx: ProcessFunction[Integer, Integer]#Context, out: Collector[Integer]): Unit = {
      out.collect(value)
    }
}

通过传递合适的参数并验证输出，对使用 ProcessFunctionTestHarnesses 是很容易进行单元测试并验证输出。

Java

public class PassThroughProcessFunctionTest {

    @Test
    public void testPassThrough() throws Exception {

        //instantiate user-defined function
        PassThroughProcessFunction processFunction = new PassThroughProcessFunction();

        // wrap user defined function into a the corresponding operator
        OneInputStreamOperatorTestHarness<Integer, Integer> harness = ProcessFunctionTestHarnesses
        	.forProcessFunction(processFunction);

        //push (timestamped) elements into the operator (and hence user defined function)
        harness.processElement(1, 10);

        //retrieve list of emitted records for assertions
        assertEquals(harness.extractOutputValues(), Collections.singletonList(1));
    }
}

Scala

class PassThroughProcessFunctionTest extends FlatSpec with Matchers {

  "PassThroughProcessFunction" should "forward values" in {

    //instantiate user-defined function
    val processFunction = new PassThroughProcessFunction

    // wrap user defined function into a the corresponding operator
    val harness = ProcessFunctionTestHarnesses.forProcessFunction(processFunction)

    //push (timestamped) elements into the operator (and hence user defined function)
    harness.processElement(1, 10)

    //retrieve list of emitted records for assertions
    harness.extractOutputValues() should contain (1)
  }
}

有关如何使用 ProcessFunctionTestHarnesses 来测试 ProcessFunction 不同风格的更多示例，, 例如 KeyedProcessFunction，KeyedCoProcessFunction，BroadcastProcessFunction等，鼓励用户自行查看 ProcessFunctionTestHarnessesTest。

测试 Flink 作业 #

JUnit 规则 `MiniClusterWithClientResource` #

Apache Flink 提供了一个名为 MiniClusterWithClientResource 的 Junit 规则，用于针对本地嵌入式小型集群测试完整的作业。叫做 MiniClusterWithClientResource.

要使用 MiniClusterWithClientResource，需要添加一个额外的依赖项（测试范围）。

<dependency>
    <groupId>org.apache.flink</groupId>
    <artifactId>flink-test-utils</artifactId>
    <version>1.20.0</version>    
    <scope>test</scope>
</dependency>

让我们采用与前面几节相同的简单 MapFunction来做示例。

Java

public class IncrementMapFunction implements MapFunction<Long, Long> {

    @Override
    public Long map(Long record) throws Exception {
        return record + 1;
    }
}

Scala

class IncrementMapFunction extends MapFunction[Long, Long] {

    override def map(record: Long): Long = {
        record + 1
    }
}

现在，可以在本地 Flink 集群使用这个 MapFunction 的简单 pipeline，如下所示。

Java

public class ExampleIntegrationTest {

     @ClassRule
     public static MiniClusterWithClientResource flinkCluster =
         new MiniClusterWithClientResource(
             new MiniClusterResourceConfiguration.Builder()
                 .setNumberSlotsPerTaskManager(2)
                 .setNumberTaskManagers(1)
                 .build());

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

        // configure your test environment
        env.setParallelism(2);

        // 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 IncrementMapFunction())
                .addSink(new CollectSink());

        // execute
        env.execute();

        // verify your results
        assertTrue(CollectSink.values.containsAll(2L, 22L, 23L));
    }

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

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

        @Override
        public void invoke(Long value, SinkFunction.Context context) throws Exception {
            values.add(value);
        }
    }
}

Scala

class StreamingJobIntegrationTest extends FlatSpec with Matchers with BeforeAndAfter {

  val flinkCluster = new MiniClusterWithClientResource(new MiniClusterResourceConfiguration.Builder()
    .setNumberSlotsPerTaskManager(2)
    .setNumberTaskManagers(1)
    .build)

  before {
    flinkCluster.before()
  }

  after {
    flinkCluster.after()
  }


  "IncrementFlatMapFunction pipeline" should "incrementValues" in {

    val env = StreamExecutionEnvironment.getExecutionEnvironment

    // configure your test environment
    env.setParallelism(2)

    // 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 IncrementMapFunction())
       .addSink(new CollectSink())

    // execute
    env.execute()

    // verify your results
    CollectSink.values should contain allOf (2, 22, 23)
    }
}

// create a testing sink
class CollectSink extends SinkFunction[Long] {

  override def invoke(value: Long, context: SinkFunction.Context): Unit = {
    CollectSink.values.add(value)
  }
}

object CollectSink {
    // must be static
    val values: util.List[Long] = Collections.synchronizedList(new util.ArrayList())
}

关于使用 MiniClusterWithClientResource 进行集成测试的几点备注：

为了不将整个 pipeline 代码从生产复制到测试，请将你的 source 和 sink 在生产代码中设置成可插拔的，并在测试中注入特殊的测试 source 和测试 sink。
这里使用 CollectSink 中的静态变量，是因为Flink 在将所有算子分布到整个集群之前先对其进行了序列化。解决此问题的一种方法是与本地 Flink 小型集群通过实例化算子的静态变量进行通信。或者，你可以使用测试的 sink 将数据写入临时目录的文件中。
如果你的作业使用事件时间计时器，则可以实现自定义的并行源函数来发出 watermark。
建议始终以 parallelism > 1 的方式在本地测试 pipeline，以识别只有在并行执行 pipeline 时才会出现的 bug。
优先使用 @ClassRule 而不是 @Rule，这样多个测试可以共享同一个 Flink 集群。这样做可以节省大量的时间，因为 Flink 集群的启动和关闭通常会占用实际测试的执行时间。
如果你的 pipeline 包含自定义状态处理，则可以通过启用 checkpoint 并在小型集群中重新启动作业来测试其正确性。为此，你需要在 pipeline 中（仅测试）抛出用户自定义函数的异常来触发失败。

测试 #

测试用户自定义函数 #

单元测试无状态、无时间限制的 UDF #

对有状态或及时 UDF 和自定义算子进行单元测试 #

单元测试 Process Function #

测试 Flink 作业 #

JUnit 规则 MiniClusterWithClientResource #

JUnit 规则 `MiniClusterWithClientResource` #