    def test_data_collection_output_schema_invalid(self):
        """
        target: test output() API for invalid scenario
        method: 1. Output node not callable  2. Output invalid type(list)
                3. Output invalid type(set)  4. Output invalid type(number)
        expected: raise exception
        """
        # 1. Output node not callable
        try:
            towhee.pipe.input('a').map('a', 'b', lambda x: x+1).output('b', 'c')
        except Exception as e:
            assert "not declared" in str(e)

        # 2. Output invalid type(list)
        try:
            towhee.pipe.input('a').map('a', 'b', lambda x: x + 1).output(['b'])
        except Exception as e:
            assert "schema must be string" in str(e)

        # 3. Output invalid type(set)
        try:
            towhee.pipe.input('a').map('a', 'b', lambda x: x + 1).output({'b'})
        except Exception as e:
            assert "schema must be string" in str(e)

        # 4. Output invalid type(number)
        try:
            towhee.pipe.input('a').map('a', 'b', lambda x: x + 1).output(0)
        except Exception as e:
            assert "schema must be string" in str(e)

        return True
target: test output() API for invalid scenario
method: 1. Output node not callable  2. Output invalid type(list)
3. Output invalid type(set)  4. Output invalid type(number)
expected: raise exception
tests/testcases/test_data_collection.py