@Override
    public OM apply(M message) {
      return this.mapFn.apply(message);
    }
the task assignment looks like the following:

input1 -----> task0, task1 -----> int1
                                   ^
input2 ------> task1, task2--------|
                                   v
input3 ------> task1 -----------> int2
samza-core/src/test/java/org/apache/samza/operators/impl/TestOperatorImplGraph.java