The first solution, mock_a().method_a.return_value, invokes mock_a in such a way that mock_a.assert_called() becomes true even if mock_a is never invoked by the code being tested.
oython returns magicmock object instead of return_value, lython returns magicmock object instead of return_value, -ython returns magicmock object instead of return_value, 0ython returns magicmock object instead of return_value, ptthon returns magicmock object instead of return_value, pgthon returns magicmock object instead of return_value, phthon returns magicmock object instead of return_value, puthon returns magicmock object instead of return_value, p7thon returns magicmock object instead of return_value, p6thon returns magicmock object instead of return_value, pyrhon returns magicmock object instead of return_value, pyfhon returns magicmock object instead of return_value, pyghon returns magicmock object instead of return_value, pyyhon returns magicmock object instead of return_value, py6hon returns magicmock object instead of return_value, py5hon returns magicmock object instead of return_value, pytgon returns magicmock object instead of return_value, pytbon returns magicmock object instead of return_value, pytnon returns magicmock object instead of return_value, pytjon returns magicmock object instead of return_value, pytuon returns magicmock object instead of return_value, pytyon returns magicmock object instead of return_value, pythin returns magicmock object instead of return_value, pythkn returns magicmock object instead of return_value, pythln returns magicmock object instead of return_value, pythpn returns magicmock object instead of return_value, pyth0n returns magicmock object instead of return_value, pyth9n returns magicmock object instead of return_value, pythob returns magicmock object instead of return_value, pythom returns magicmock object instead of return_value, pythoj returns magicmock object instead of return_value, pythoh returns magicmock object instead of return_value, python eeturns magicmock object instead of return_value, python deturns magicmock object instead of return_value, python feturns magicmock object instead of return_value, python teturns magicmock object instead of return_value, python 5eturns magicmock object instead of return_value, python 4eturns magicmock object instead of return_value, python rwturns magicmock object instead of return_value, python rsturns magicmock object instead of return_value, python rdturns magicmock object instead of return_value, python rrturns magicmock object instead of return_value, python r4turns magicmock object instead of return_value, python r3turns magicmock object instead of return_value, python rerurns magicmock object instead of return_value, python refurns magicmock object instead of return_value, python regurns magicmock object instead of return_value, python reyurns magicmock object instead of return_value, python re6urns magicmock object instead of return_value, python re5urns magicmock object instead of return_value, python retyrns magicmock object instead of return_value, python rethrns magicmock object instead of return_value, python retjrns magicmock object instead of return_value, python retirns magicmock object instead of return_value, python ret8rns magicmock object instead of return_value, python ret7rns magicmock object instead of return_value, python retuens magicmock object instead of return_value, python retudns magicmock object instead of return_value, python retufns magicmock object instead of return_value, python retutns magicmock object instead of return_value, python retu5ns magicmock object instead of return_value, python retu4ns magicmock object instead of return_value, python returbs magicmock object instead of return_value, python returms magicmock object instead of return_value, python returjs magicmock object instead of return_value, python returhs magicmock object instead of return_value, python returna magicmock object instead of return_value, python returnz magicmock object instead of return_value, python returnx magicmock object instead of return_value, python returnd magicmock object instead of return_value, python returne magicmock object instead of return_value, python returnw magicmock object instead of return_value, python returns nagicmock object instead of return_value, python returns kagicmock object instead of return_value, python returns jagicmock object instead of return_value, python returns mzgicmock object instead of return_value, python returns msgicmock object instead of return_value, python returns mwgicmock object instead of return_value, python returns mqgicmock object instead of return_value, python returns maficmock object instead of return_value, python returns mavicmock object instead of return_value, python returns mabicmock object instead of return_value, python returns mahicmock object instead of return_value, python returns mayicmock object instead of return_value, python returns maticmock object instead of return_value, python returns magucmock object instead of return_value, python returns magjcmock object instead of return_value, python returns magkcmock object instead of return_value, python returns magocmock object instead of return_value, python returns mag9cmock object instead of return_value, python returns mag8cmock object instead of return_value, python returns magixmock object instead of return_value, python returns magivmock object instead of return_value, python returns magifmock object instead of return_value, python returns magidmock object instead of return_value, python returns magicnock object instead of return_value, python returns magickock object instead of return_value, python returns magicjock object instead of return_value, python returns magicmick object instead of return_value, python returns magicmkck object instead of return_value, python returns magicmlck object instead of return_value, python returns magicmpck object instead of return_value, python returns magicm0ck object instead of return_value, python returns magicm9ck object instead of return_value, python returns magicmoxk object instead of return_value, python returns magicmovk object instead of return_value, python returns magicmofk object instead of return_value, python returns magicmodk object instead of return_value, python returns magicmocj object instead of return_value, python returns magicmocm object instead of return_value, python returns magicmocl object instead of return_value, python returns magicmoco object instead of return_value, python returns magicmoci object instead of return_value, python returns magicmock ibject instead of return_value, python returns magicmock kbject instead of return_value, python returns magicmock lbject instead of return_value, python returns magicmock pbject instead of return_value, python returns magicmock 0bject instead of return_value, python returns magicmock 9bject instead of return_value, python returns magicmock ovject instead of return_value