Test failures with pytest 5+

[FRidh]

============================= test session starts ==============================
platform linux -- Python 3.7.4, pytest-5.1.0, py-1.8.0, pluggy-0.12.0
rootdir: /build/source
collected 332 items

datashape/tests/test_coretypes.py ...................................... [ 11%]
....................................xx.................................. [ 33%]
.xxxx...............................                                     [ 43%]
datashape/tests/test_creation.py ..x..............xx...                  [ 50%]
datashape/tests/test_discovery.py ...................................... [ 62%]
.......x..                                                               [ 65%]
datashape/tests/test_lexer.py .....                                      [ 66%]
datashape/tests/test_operations.py ...                                   [ 67%]
datashape/tests/test_parser.py ...............................           [ 76%]
datashape/tests/test_predicates.py ....                                  [ 78%]
datashape/tests/test_promote.py ........................                 [ 85%]
datashape/tests/test_typeset.py ......                                   [ 87%]
datashape/tests/test_util.py .............................               [ 95%]
datashape/tests/test_version.py .                                        [ 96%]
datashape/util/tests/test_testing.py ..FF.........                       [100%]

=================================== FAILURES ===================================
_________________________________ test_record __________________________________

    def test_record():
        assert_dshape_equal(
            R['a': int32, 'b': float32],
            R['a': int32, 'b': float32],
        )
    
        with pytest.raises(AssertionError) as e:
            assert_dshape_equal(
                R['a': int32, 'b': float32],
                R['a': int32, 'b': int32],
            )
>       assert "'float32' != 'int32'" in str(e)
E       assert "'float32' != 'int32'" in '<ExceptionInfo AssertionError tblen=5>'
E        +  where '<ExceptionInfo AssertionError tblen=5>' = str(<ExceptionInfo AssertionError tblen=5>)

datashape/util/tests/test_testing.py:80: AssertionError
__________________________________ test_tuple __________________________________

    def test_tuple():
        assert_dshape_equal(Tuple((int32, float32)), Tuple((int32, float32)))
    
        with pytest.raises(AssertionError) as e:
            assert_dshape_equal(Tuple((int32, float32)), Tuple((int32, int32)))
>       assert "'float32' != 'int32'" in str(e)
E       assert "'float32' != 'int32'" in '<ExceptionInfo AssertionError tblen=7>'
E        +  where '<ExceptionInfo AssertionError tblen=7>' = str(<ExceptionInfo AssertionError tblen=7>)

datashape/util/tests/test_testing.py:127: AssertionError
=============================== warnings summary ===============================