Code review comment: Actually, `isEmpty` is not implemented :smile: There are just too many ways of checking if a collection is empty or not

Code under review:
public void testBasicInfo() {
        TestingOneInputStreamOperator inOperator1 = new TestingOneInputStreamOperator();
        TestingOneInputStreamOperator inOperator2 = new TestingOneInputStreamOperator();
        TestingTwoInputStreamOperator outOperator = new TestingTwoInputStreamOperator();
        TableOperatorWrapper<TestingOneInputStreamOperator> wrapper1 =
                createOneInputOperatorWrapper(inOperator1, "test1");

        TableOperatorWrapper<TestingOneInputStreamOperator> wrapper2 =
                createOneInputOperatorWrapper(inOperator2, "test2");

        TableOperatorWrapper<TestingTwoInputStreamOperator> wrapper3 =
                createTwoInputOperatorWrapper(outOperator, "test3");
        wrapper3.addInput(wrapper1, 1);
        wrapper3.addInput(wrapper2, 2);

        assertThat(wrapper1.getInputEdges().isEmpty()).isTrue();
        assertThat(wrapper1.getInputWrappers().isEmpty()).isTrue();
        assertThat(wrapper1.getOutputWrappers()).containsExactly(wrapper3);
        assertThat(wrapper1.getOutputEdges()).containsExactly(new Edge(wrapper1, wrapper3, 1));

        assertThat(wrapper2.getInputEdges().isEmpty()).isTrue();
        assertThat(wrapper2.getInputWrappers().isEmpty()).isTrue();
        assertThat(wrapper2.getOutputWrappers()).containsExactly(wrapper3);
        assertThat(wrapper2.getOutputEdges()).containsExactly(new Edge(wrapper2, wrapper3, 2));

        assertThat(wrapper3.getOutputEdges().isEmpty()).isTrue();
        assertThat(wrapper3.getOutputWrappers().isEmpty()).isTrue();
        assertThat(wrapper3.getInputWrappers()).isEqualTo(Arrays.asList(wrapper1, wrapper2));
        assertThat(wrapper3.getInputEdges())
                .isEqualTo(
                        Arrays.asList(
                                new Edge(wrapper1, wrapper3, 1), new Edge(wrapper2, wrapper3, 2)));
    }

Line commented on: assertThat(wrapper2.getInputWrappers().isEmpty()).isTrue();

Revised code:
public void testBasicInfo() {
        TestingOneInputStreamOperator inOperator1 = new TestingOneInputStreamOperator();
        TestingOneInputStreamOperator inOperator2 = new TestingOneInputStreamOperator();
        TestingTwoInputStreamOperator outOperator = new TestingTwoInputStreamOperator();
        TableOperatorWrapper<TestingOneInputStreamOperator> wrapper1 =
                createOneInputOperatorWrapper(inOperator1, "test1");

        TableOperatorWrapper<TestingOneInputStreamOperator> wrapper2 =
                createOneInputOperatorWrapper(inOperator2, "test2");

        TableOperatorWrapper<TestingTwoInputStreamOperator> wrapper3 =
                createTwoInputOperatorWrapper(outOperator, "test3");
        wrapper3.addInput(wrapper1, 1);
        wrapper3.addInput(wrapper2, 2);

        assertThat(wrapper1.getInputEdges()).isEmpty();
        assertThat(wrapper1.getInputWrappers()).isEmpty();
        assertThat(wrapper1.getOutputWrappers()).containsExactly(wrapper3);
        assertThat(wrapper1.getOutputEdges()).containsExactly(new Edge(wrapper1, wrapper3, 1));

        assertThat(wrapper2.getInputEdges()).isEmpty();
        assertThat(wrapper2.getInputWrappers()).isEmpty();
        assertThat(wrapper2.getOutputWrappers()).containsExactly(wrapper3);
        assertThat(wrapper2.getOutputEdges()).containsExactly(new Edge(wrapper2, wrapper3, 2));

        assertThat(wrapper3.getOutputEdges()).isEmpty();
        assertThat(wrapper3.getOutputWrappers()).isEmpty();
        assertThat(wrapper3.getInputWrappers()).isEqualTo(Arrays.asList(wrapper1, wrapper2));
        assertThat(wrapper3.getInputEdges())
                .isEqualTo(
                        Arrays.asList(
                                new Edge(wrapper1, wrapper3, 1), new Edge(wrapper2, wrapper3, 2)));
    }