Test the behavior of late events

src/test/java/com/ververica/flinktraining/exercises/datastream_java/process/ExpiringStateHarnessTest.java

@@ -20,6 +20,7 @@
 import org.apache.flink.api.java.tuple.Tuple2;
 import org.apache.flink.streaming.api.operators.co.KeyedCoProcessOperator;
 
+import org.apache.flink.streaming.api.watermark.Watermark;
 import org.apache.flink.streaming.runtime.streamrecord.StreamRecord;
 import org.apache.flink.streaming.util.KeyedTwoInputStreamOperatorTestHarness;
 import org.apache.flink.streaming.util.TestHarnessUtil;
@@ -58,6 +59,51 @@ public void testRideThenFare() throws Exception {
 		assert(harness.numEventTimeTimers() == 0);
 	}
 
+	@Test
+	public void testLateEvent() throws Exception {
+		KeyedTwoInputStreamOperatorTestHarness<Long, TaxiRide, TaxiFare, Tuple2<TaxiRide, TaxiFare>> harness = setupHarness();
+
+		final TaxiRide ride1 = testRide(1);
+		final TaxiFare fare1 = testFare(1);
+
+		harness.processElement1(new StreamRecord<>(ride1, 0));
+
+		// Check that 1 state and 1 timers are created for the ride event
+		assert(harness.numKeyedStateEntries() == 1);
+		assert(harness.numEventTimeTimers() == 1);
+
+		// advance the ride & fare watermark
+		harness.processBothWatermarks(new Watermark(1));
+
+		// Check that no state or timers are left behind
+		assert(harness.numKeyedStateEntries() == 0);
+		assert(harness.numEventTimeTimers() == 0);
+
+		// push a late fare event
+		harness.processElement2(new StreamRecord<>(fare1, 2));
+
+		// Check that 1 state and 1 timers are created for the late fare event
+		assert(harness.numKeyedStateEntries() == 1);
+		assert(harness.numEventTimeTimers() == 1);
+
+		// advance the side & fare watermark
+		harness.processBothWatermarks(new Watermark(2));
+
+		// Check that no state or timers are left behind
+		assert(harness.numKeyedStateEntries() == 0);
+		assert(harness.numEventTimeTimers() == 0);
+
+		ConcurrentLinkedQueue<Object> expectedOutput = new ConcurrentLinkedQueue<>();
+		expectedOutput.add(new Watermark(1));
+		expectedOutput.add(new Watermark(2));
+
+		// Check that the result contains only two watermarks as the unmatched (due to lateness) events are sent to side output
+		ConcurrentLinkedQueue<Object> actualOutput = harness.getOutput();
+		TestHarnessUtil.assertOutputEquals("Output was not correct.", expectedOutput, actualOutput);
+
+	}
+
+
 	private TaxiRide testRide(long rideId) {
 		return new TaxiRide(rideId, true, new DateTime(0), new DateTime(0),
 				0F, 0F, 0F, 0F, (short)1, 0, rideId);