pytest does not print chained exception for python 3

[jettify]

py.test pytest (2.8.5) does not print chained exceptions, data located in e.__cause__ and e.__context__.

If I execute this little script using python3 (python3 test_exception.py):

def test_x():
    try:
        raise KeyError
    except Exception as e:
        raise RuntimeError from e

if __name__ == '__main__':
    test_x()

I get:

Traceback (most recent call last):
  File "py_test.py", line 4, in test_x
    raise KeyError
KeyError

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "py_test.py", line 9, in <module>
    test_x()
  File "py_test.py", line 6, in test_x
    raise RuntimeError from e
RuntimeError

in case of py.test (py.test test_exception.py):

    def test_x():
        try:
            raise KeyError
        except Exception as e:
>           raise RuntimeError from e
E           RuntimeError

py_test.py:6: RuntimeError

[nicoddemus]

Thanks @jettify!

Closing as a duplicate of #138 though.

This should be tackled soon, because what was blocking this issue was #103, which is a working in progress at #1199.