Package org.apache.flink.testutils.junit

Class SharedObjects

java.lang.Object
org.junit.rules.ExternalResource
org.apache.flink.testutils.junit.SharedObjects
All Implemented Interfaces:
org.junit.rules.TestRule
@NotThreadSafe public class SharedObjects extends org.junit.rules.ExternalResource
This rule allows objects to be used both in the main test case as well as in UDFs by using serializable SharedReferences. Usage: 

    @Rule
     public final SharedObjects sharedObjects = SharedObjects.create();

    @Test
     public void test() throws Exception {
         StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();
        SharedReference<Queue<Long>> listRef = sharedObjects.add(new ConcurrentLinkedQueue<>());
         int n = 10000;
         env.setParallelism(100);
         env.fromSequence(0, n).map(i -> listRef.get().add(i));
         env.execute();
         assertEquals(n + 1, listRef.get().size());
         assertEquals(
                 LongStream.rangeClosed(0, n).boxed().collect(Collectors.toList()),
                 listRef.get().stream().sorted().collect(Collectors.toList()));
     }

The main idea is that shared objects are bound to the scope of a test case instead of a class. That allows us to:

  • Avoid all kinds of static fields in test classes that only exist since all fields in UDFs need to be serializable.
  • Hopefully make it easier to reason about the test setup
  • Facilitate to share more test building blocks across test classes.
  • Fully allow tests to be rerun/run in parallel without worrying about static fields

Note that since the shared objects are accessed through multiple threads, they need to be thread-safe or accessed in a thread-safe manner.

  • Method Details

    • create

      public static SharedObjects create()
      Creates a new instance. Usually that should be done inside a JUnit test class as an instance-field annotated with Rule.

    • add

      public <T> SharedReference<T> add(T object)
      Adds a new object to this SharedObjects. Although not necessary, it is recommended to only access the object through the returned SharedReference.

    • before

      protected void before() throws Throwable
      Overrides:
      before in class org.junit.rules.ExternalResource
      Throws:
      Throwable

    • after

      protected void after()
      Overrides:
      after in class org.junit.rules.ExternalResource

    • equals

      public boolean equals(Object o)
      Overrides:
      equals in class Object

    • hashCode

      public int hashCode()
      Overrides:
      hashCode in class Object