Implementing Checkpointed interface: snapshotState() in flink is not being called - apache-flink

Question

I have created a test below. I am testing snapshots. I supposed that snapshotState and restoreState should be called but it seems that it is not happening. Why?
The main code:
public class CheckpointedTest {
public static void main(String[] args) throws Exception {
StreamExecutionEnvironment env =
StreamExecutionEnvironment.getExecutionEnvironment();
env.enableCheckpointing(5000);
env.setParallelism(2);
List<Integer> list = new ArrayList<Integer>();
for (int i = 0; i < 10; i++) {
list.add(i);
}
DataStream<Integer> test = env.fromCollection(list);
test.map(new CheckpointedFunction());
env.execute();
}
}
The function implementation is the following:
public class CheckpointedFunction implements MapFunction<Integer, Integer>, Checkpointed<Integer> {
private Integer count = 0;
#Override
public Integer map(Integer value) throws Exception {
System.out.println("count: " + count);
Thread.sleep((long) (Math.random()*4000));
return count++;
}
#Override
public Integer snapshotState(long checkpointId, long checkpointTimestamp) throws Exception {
System.out.println("Snapshot count: " + count);
return count;
}
#Override
public void restoreState(Integer state) throws Exception {
this.count = state;
System.out.println("Restored count: " + count);
}
}