    def test_data_collection_concat_invalid(self):
        """
        target: test concat() API for invalid scenario
        method: 1. Concat pipe not existed
                2. Concat pipelines which have conflicting apis
                3. concat empty
        expected: raise exception
        """
        # 1. Concat pipe not existed
        try:
            pipe0 = towhee.pipe.input('a', 'b', 'c')
            pipe2 = pipe0.map(('b', 'c'), 'e', lambda x, y: x - y)
            pipe2.concat(pipe).output('d', 'e')
        except Exception as e:
            assert "the parameter of concat must be Pipeline" in str(e)

        # 3. Concat pipelines which have conflicting apis
        try:
            pipe0 = towhee.pipe.input('a')
            pipe1 = pipe0.map('a', 'b', lambda x: x + 1).output('b')
            pipe2 = pipe0.map('a', 'c', lambda x: x + 2).output('c')
            towhee.pipe.concat(pipe1, pipe2).output('b', 'c')
        except Exception as e:
            assert "has no attribute" in str(e)

        # 4. concat empty
        try:
            pipe4 = towhee.pipe.input('a').map('a', 'b', lambda x: x + 1)
            pipe4.concat().output('b')
        except Exception as e:
            assert "The parameter of concat cannot be None" in str(e)

        return True
target: test concat() API for invalid scenario
method: 1. Concat pipe not existed
2. Concat pipelines which have conflicting apis
3. concat empty
expected: raise exception
tests/testcases/test_data_collection.py