Demo of Python failure reports with pytest

Here is a nice run of several tens of failures and how pytest presents things (unfortunately not showing the nice colors here in the HTML that you get on the terminal - we are working on that):

assertion $ pytest failure_demo.py
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-3.x.y, py-1.x.y, pluggy-0.x.y
rootdir: $REGENDOC_TMPDIR/assertion, inifile:
collected 42 items

failure_demo.py FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF           [100%]

================================= FAILURES =================================
____________________________ test_generative[0] ____________________________

param1 = 3, param2 = 6

    def test_generative(param1, param2):
>       assert param1 * 2 < param2
E       assert (3 * 2) < 6

failure_demo.py:19: AssertionError
_________________________ TestFailing.test_simple __________________________

self = <failure_demo.TestFailing object at 0xdeadbeef>

    def test_simple(self):
        def f():
            return 42

        def g():
            return 43

>       assert f() == g()
E       assert 42 == 43
E        +  where 42 = <function TestFailing.test_simple.<locals>.f at 0xdeadbeef>()
E        +  and   43 = <function TestFailing.test_simple.<locals>.g at 0xdeadbeef>()

failure_demo.py:35: AssertionError
____________________ TestFailing.test_simple_multiline _____________________

self = <failure_demo.TestFailing object at 0xdeadbeef>

    def test_simple_multiline(self):
>       otherfunc_multi(42, 6 * 9)

failure_demo.py:38:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

a = 42, b = 54

    def otherfunc_multi(a, b):
>       assert a == b
E       assert 42 == 54

failure_demo.py:15: AssertionError
___________________________ TestFailing.test_not ___________________________

self = <failure_demo.TestFailing object at 0xdeadbeef>

    def test_not(self):
        def f():
            return 42

>       assert not f()
E       assert not 42
E        +  where 42 = <function TestFailing.test_not.<locals>.f at 0xdeadbeef>()

failure_demo.py:44: AssertionError
_________________ TestSpecialisedExplanations.test_eq_text _________________

self = <failure_demo.TestSpecialisedExplanations object at 0xdeadbeef>

    def test_eq_text(self):
>       assert "spam" == "eggs"
E       AssertionError: assert 'spam' == 'eggs'
E         - spam
E         + eggs

failure_demo.py:49: AssertionError
_____________ TestSpecialisedExplanations.test_eq_similar_text _____________

self = <failure_demo.TestSpecialisedExplanations object at 0xdeadbeef>

    def test_eq_similar_text(self):
>       assert "foo 1 bar" == "foo 2 bar"
E       AssertionError: assert 'foo 1 bar' == 'foo 2 bar'
E         - foo 1 bar
E         ?     ^
E         + foo 2 bar
E         ?     ^

failure_demo.py:52: AssertionError
____________ TestSpecialisedExplanations.test_eq_multiline_text ____________

self = <failure_demo.TestSpecialisedExplanations object at 0xdeadbeef>

    def test_eq_multiline_text(self):
>       assert "foo\nspam\nbar" == "foo\neggs\nbar"
E       AssertionError: assert 'foo\nspam\nbar' == 'foo\neggs\nbar'
E           foo
E         - spam
E         + eggs
E           bar

failure_demo.py:55: AssertionError
______________ TestSpecialisedExplanations.test_eq_long_text _______________

self = <failure_demo.TestSpecialisedExplanations object at 0xdeadbeef>

    def test_eq_long_text(self):
        a = "1" * 100 + "a" + "2" * 100
        b = "1" * 100 + "b" + "2" * 100
>       assert a == b
E       AssertionError: assert '111111111111...2222222222222' == '1111111111111...2222222222222'
E         Skipping 90 identical leading characters in diff, use -v to show
E         Skipping 91 identical trailing characters in diff, use -v to show
E         - 1111111111a222222222
E         ?           ^
E         + 1111111111b222222222
E         ?           ^

failure_demo.py:60: AssertionError
_________ TestSpecialisedExplanations.test_eq_long_text_multiline __________

self = <failure_demo.TestSpecialisedExplanations object at 0xdeadbeef>

    def test_eq_long_text_multiline(self):
        a = "1\n" * 100 + "a" + "2\n" * 100
        b = "1\n" * 100 + "b" + "2\n" * 100
>       assert a == b
E       AssertionError: assert '1\n1\n1\n1\n...n2\n2\n2\n2\n' == '1\n1\n1\n1\n1...n2\n2\n2\n2\n'
E         Skipping 190 identical leading characters in diff, use -v to show
E         Skipping 191 identical trailing characters in diff, use -v to show
E           1
E           1
E           1
E           1
E           1...
E
E         ...Full output truncated (7 lines hidden), use '-vv' to show

failure_demo.py:65: AssertionError
_________________ TestSpecialisedExplanations.test_eq_list _________________

self = <failure_demo.TestSpecialisedExplanations object at 0xdeadbeef>

    def test_eq_list(self):
>       assert [0, 1, 2] == [0, 1, 3]
E       assert [0, 1, 2] == [0, 1, 3]
E         At index 2 diff: 2 != 3
E         Use -v to get the full diff

failure_demo.py:68: AssertionError
______________ TestSpecialisedExplanations.test_eq_list_long _______________

self = <failure_demo.TestSpecialisedExplanations object at 0xdeadbeef>

    def test_eq_list_long(self):
        a = [0] * 100 + [1] + [3] * 100
        b = [0] * 100 + [2] + [3] * 100
>       assert a == b
E       assert [0, 0, 0, 0, 0, 0, ...] == [0, 0, 0, 0, 0, 0, ...]
E         At index 100 diff: 1 != 2
E         Use -v to get the full diff

failure_demo.py:73: AssertionError
_________________ TestSpecialisedExplanations.test_eq_dict _________________

self = <failure_demo.TestSpecialisedExplanations object at 0xdeadbeef>

    def test_eq_dict(self):
>       assert {"a": 0, "b": 1, "c": 0} == {"a": 0, "b": 2, "d": 0}
E       AssertionError: assert {'a': 0, 'b': 1, 'c': 0} == {'a': 0, 'b': 2, 'd': 0}
E         Omitting 1 identical items, use -vv to show
E         Differing items:
E         {'b': 1} != {'b': 2}
E         Left contains more items:
E         {'c': 0}
E         Right contains more items:
E         {'d': 0}...
E
E         ...Full output truncated (2 lines hidden), use '-vv' to show

failure_demo.py:76: AssertionError
_________________ TestSpecialisedExplanations.test_eq_set __________________

self = <failure_demo.TestSpecialisedExplanations object at 0xdeadbeef>

    def test_eq_set(self):
>       assert {0, 10, 11, 12} == {0, 20, 21}
E       AssertionError: assert {0, 10, 11, 12} == {0, 20, 21}
E         Extra items in the left set:
E         10
E         11
E         12
E         Extra items in the right set:
E         20
E         21...
E
E         ...Full output truncated (2 lines hidden), use '-vv' to show

failure_demo.py:79: AssertionError
_____________ TestSpecialisedExplanations.test_eq_longer_list ______________

self = <failure_demo.TestSpecialisedExplanations object at 0xdeadbeef>

    def test_eq_longer_list(self):
>       assert [1, 2] == [1, 2, 3]
E       assert [1, 2] == [1, 2, 3]
E         Right contains more items, first extra item: 3
E         Use -v to get the full diff

failure_demo.py:82: AssertionError
_________________ TestSpecialisedExplanations.test_in_list _________________

self = <failure_demo.TestSpecialisedExplanations object at 0xdeadbeef>

    def test_in_list(self):
>       assert 1 in [0, 2, 3, 4, 5]
E       assert 1 in [0, 2, 3, 4, 5]

failure_demo.py:85: AssertionError
__________ TestSpecialisedExplanations.test_not_in_text_multiline __________

self = <failure_demo.TestSpecialisedExplanations object at 0xdeadbeef>

    def test_not_in_text_multiline(self):
        text = "some multiline\ntext\nwhich\nincludes foo\nand a\ntail"
>       assert "foo" not in text
E       AssertionError: assert 'foo' not in 'some multiline\ntext\nw...ncludes foo\nand a\ntail'
E         'foo' is contained here:
E           some multiline
E           text
E           which
E           includes foo
E         ?          +++
E           and a...
E
E         ...Full output truncated (2 lines hidden), use '-vv' to show

failure_demo.py:89: AssertionError
___________ TestSpecialisedExplanations.test_not_in_text_single ____________

self = <failure_demo.TestSpecialisedExplanations object at 0xdeadbeef>

    def test_not_in_text_single(self):
        text = "single foo line"
>       assert "foo" not in text
E       AssertionError: assert 'foo' not in 'single foo line'
E         'foo' is contained here:
E           single foo line
E         ?        +++

failure_demo.py:93: AssertionError
_________ TestSpecialisedExplanations.test_not_in_text_single_long _________

self = <failure_demo.TestSpecialisedExplanations object at 0xdeadbeef>

    def test_not_in_text_single_long(self):
        text = "head " * 50 + "foo " + "tail " * 20
>       assert "foo" not in text
E       AssertionError: assert 'foo' not in 'head head head head hea...ail tail tail tail tail '
E         'foo' is contained here:
E           head head foo tail tail tail tail tail tail tail tail tail tail tail tail tail tail tail tail tail tail tail tail
E         ?           +++

failure_demo.py:97: AssertionError
______ TestSpecialisedExplanations.test_not_in_text_single_long_term _______

self = <failure_demo.TestSpecialisedExplanations object at 0xdeadbeef>

    def test_not_in_text_single_long_term(self):
        text = "head " * 50 + "f" * 70 + "tail " * 20
>       assert "f" * 70 not in text
E       AssertionError: assert 'fffffffffff...ffffffffffff' not in 'head head he...l tail tail '
E         'ffffffffffffffffff...fffffffffffffffffff' is contained here:
E           head head fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffftail tail tail tail tail tail tail tail tail tail tail tail tail tail tail tail tail tail tail tail
E         ?           ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

failure_demo.py:101: AssertionError
______________________________ test_attribute ______________________________

    def test_attribute():
        class Foo(object):
            b = 1

        i = Foo()
>       assert i.b == 2
E       assert 1 == 2
E        +  where 1 = <failure_demo.test_attribute.<locals>.Foo object at 0xdeadbeef>.b

failure_demo.py:109: AssertionError
_________________________ test_attribute_instance __________________________

    def test_attribute_instance():
        class Foo(object):
            b = 1

>       assert Foo().b == 2
E       AssertionError: assert 1 == 2
E        +  where 1 = <failure_demo.test_attribute_instance.<locals>.Foo object at 0xdeadbeef>.b
E        +    where <failure_demo.test_attribute_instance.<locals>.Foo object at 0xdeadbeef> = <class 'failure_demo.test_attribute_instance.<locals>.Foo'>()

failure_demo.py:116: AssertionError
__________________________ test_attribute_failure __________________________

    def test_attribute_failure():
        class Foo(object):
            def _get_b(self):
                raise Exception("Failed to get attrib")

            b = property(_get_b)

        i = Foo()
>       assert i.b == 2

failure_demo.py:127:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <failure_demo.test_attribute_failure.<locals>.Foo object at 0xdeadbeef>

    def _get_b(self):
>       raise Exception("Failed to get attrib")
E       Exception: Failed to get attrib

failure_demo.py:122: Exception
_________________________ test_attribute_multiple __________________________

    def test_attribute_multiple():
        class Foo(object):
            b = 1

        class Bar(object):
            b = 2

>       assert Foo().b == Bar().b
E       AssertionError: assert 1 == 2
E        +  where 1 = <failure_demo.test_attribute_multiple.<locals>.Foo object at 0xdeadbeef>.b
E        +    where <failure_demo.test_attribute_multiple.<locals>.Foo object at 0xdeadbeef> = <class 'failure_demo.test_attribute_multiple.<locals>.Foo'>()
E        +  and   2 = <failure_demo.test_attribute_multiple.<locals>.Bar object at 0xdeadbeef>.b
E        +    where <failure_demo.test_attribute_multiple.<locals>.Bar object at 0xdeadbeef> = <class 'failure_demo.test_attribute_multiple.<locals>.Bar'>()

failure_demo.py:137: AssertionError
__________________________ TestRaises.test_raises __________________________

self = <failure_demo.TestRaises object at 0xdeadbeef>

    def test_raises(self):
        s = "qwe"  # NOQA
>       raises(TypeError, "int(s)")

failure_demo.py:147:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

>   int(s)
E   ValueError: invalid literal for int() with base 10: 'qwe'

<0-codegen $PYTHON_PREFIX/lib/python3.5/site-packages/_pytest/python_api.py:635>:1: ValueError
______________________ TestRaises.test_raises_doesnt _______________________

self = <failure_demo.TestRaises object at 0xdeadbeef>

    def test_raises_doesnt(self):
>       raises(IOError, "int('3')")
E       Failed: DID NOT RAISE <class 'OSError'>

failure_demo.py:150: Failed
__________________________ TestRaises.test_raise ___________________________

self = <failure_demo.TestRaises object at 0xdeadbeef>

    def test_raise(self):
>       raise ValueError("demo error")
E       ValueError: demo error

failure_demo.py:153: ValueError
________________________ TestRaises.test_tupleerror ________________________

self = <failure_demo.TestRaises object at 0xdeadbeef>

    def test_tupleerror(self):
>       a, b = [1]  # NOQA
E       ValueError: not enough values to unpack (expected 2, got 1)

failure_demo.py:156: ValueError
______ TestRaises.test_reinterpret_fails_with_print_for_the_fun_of_it ______

self = <failure_demo.TestRaises object at 0xdeadbeef>

    def test_reinterpret_fails_with_print_for_the_fun_of_it(self):
        items = [1, 2, 3]
        print("items is %r" % items)
>       a, b = items.pop()
E       TypeError: 'int' object is not iterable

failure_demo.py:161: TypeError
--------------------------- Captured stdout call ---------------------------
items is [1, 2, 3]
________________________ TestRaises.test_some_error ________________________

self = <failure_demo.TestRaises object at 0xdeadbeef>

    def test_some_error(self):
>       if namenotexi:  # NOQA
E       NameError: name 'namenotexi' is not defined

failure_demo.py:164: NameError
____________________ test_dynamic_compile_shows_nicely _____________________

    def test_dynamic_compile_shows_nicely():
        import imp
        import sys

        src = "def foo():\n assert 1 == 0\n"
        name = "abc-123"
        module = imp.new_module(name)
        code = _pytest._code.compile(src, name, "exec")
        py.builtin.exec_(code, module.__dict__)
        sys.modules[name] = module
>       module.foo()

failure_demo.py:182:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

    def foo():
>    assert 1 == 0
E    AssertionError

<2-codegen 'abc-123' $REGENDOC_TMPDIR/assertion/failure_demo.py:179>:2: AssertionError
____________________ TestMoreErrors.test_complex_error _____________________

self = <failure_demo.TestMoreErrors object at 0xdeadbeef>

    def test_complex_error(self):
        def f():
            return 44

        def g():
            return 43

>       somefunc(f(), g())

failure_demo.py:193:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
failure_demo.py:11: in somefunc
    otherfunc(x, y)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

a = 44, b = 43

    def otherfunc(a, b):
>       assert a == b
E       assert 44 == 43

failure_demo.py:7: AssertionError
___________________ TestMoreErrors.test_z1_unpack_error ____________________

self = <failure_demo.TestMoreErrors object at 0xdeadbeef>

    def test_z1_unpack_error(self):
        items = []
>       a, b = items
E       ValueError: not enough values to unpack (expected 2, got 0)

failure_demo.py:197: ValueError
____________________ TestMoreErrors.test_z2_type_error _____________________

self = <failure_demo.TestMoreErrors object at 0xdeadbeef>

    def test_z2_type_error(self):
        items = 3
>       a, b = items
E       TypeError: 'int' object is not iterable

failure_demo.py:201: TypeError
______________________ TestMoreErrors.test_startswith ______________________

self = <failure_demo.TestMoreErrors object at 0xdeadbeef>

    def test_startswith(self):
        s = "123"
        g = "456"
>       assert s.startswith(g)
E       AssertionError: assert False
E        +  where False = <built-in method startswith of str object at 0xdeadbeef>('456')
E        +    where <built-in method startswith of str object at 0xdeadbeef> = '123'.startswith

failure_demo.py:206: AssertionError
__________________ TestMoreErrors.test_startswith_nested ___________________

self = <failure_demo.TestMoreErrors object at 0xdeadbeef>

    def test_startswith_nested(self):
        def f():
            return "123"

        def g():
            return "456"

>       assert f().startswith(g())
E       AssertionError: assert False
E        +  where False = <built-in method startswith of str object at 0xdeadbeef>('456')
E        +    where <built-in method startswith of str object at 0xdeadbeef> = '123'.startswith
E        +      where '123' = <function TestMoreErrors.test_startswith_nested.<locals>.f at 0xdeadbeef>()
E        +    and   '456' = <function TestMoreErrors.test_startswith_nested.<locals>.g at 0xdeadbeef>()

failure_demo.py:215: AssertionError
_____________________ TestMoreErrors.test_global_func ______________________

self = <failure_demo.TestMoreErrors object at 0xdeadbeef>

    def test_global_func(self):
>       assert isinstance(globf(42), float)
E       assert False
E        +  where False = isinstance(43, float)
E        +    where 43 = globf(42)

failure_demo.py:218: AssertionError
_______________________ TestMoreErrors.test_instance _______________________

self = <failure_demo.TestMoreErrors object at 0xdeadbeef>

    def test_instance(self):
        self.x = 6 * 7
>       assert self.x != 42
E       assert 42 != 42
E        +  where 42 = <failure_demo.TestMoreErrors object at 0xdeadbeef>.x

failure_demo.py:222: AssertionError
_______________________ TestMoreErrors.test_compare ________________________

self = <failure_demo.TestMoreErrors object at 0xdeadbeef>

    def test_compare(self):
>       assert globf(10) < 5
E       assert 11 < 5
E        +  where 11 = globf(10)

failure_demo.py:225: AssertionError
_____________________ TestMoreErrors.test_try_finally ______________________

self = <failure_demo.TestMoreErrors object at 0xdeadbeef>

    def test_try_finally(self):
        x = 1
        try:
>           assert x == 0
E           assert 1 == 0

failure_demo.py:230: AssertionError
___________________ TestCustomAssertMsg.test_single_line ___________________

self = <failure_demo.TestCustomAssertMsg object at 0xdeadbeef>

    def test_single_line(self):
        class A(object):
            a = 1

        b = 2
>       assert A.a == b, "A.a appears not to be b"
E       AssertionError: A.a appears not to be b
E       assert 1 == 2
E        +  where 1 = <class 'failure_demo.TestCustomAssertMsg.test_single_line.<locals>.A'>.a

failure_demo.py:241: AssertionError
____________________ TestCustomAssertMsg.test_multiline ____________________

self = <failure_demo.TestCustomAssertMsg object at 0xdeadbeef>

    def test_multiline(self):
        class A(object):
            a = 1

        b = 2
>       assert (
            A.a == b
        ), "A.a appears not to be b\n" "or does not appear to be b\none of those"
E       AssertionError: A.a appears not to be b
E         or does not appear to be b
E         one of those
E       assert 1 == 2
E        +  where 1 = <class 'failure_demo.TestCustomAssertMsg.test_multiline.<locals>.A'>.a

failure_demo.py:248: AssertionError
___________________ TestCustomAssertMsg.test_custom_repr ___________________

self = <failure_demo.TestCustomAssertMsg object at 0xdeadbeef>

    def test_custom_repr(self):
        class JSON(object):
            a = 1

            def __repr__(self):
                return "This is JSON\n{\n  'foo': 'bar'\n}"

        a = JSON()
        b = 2
>       assert a.a == b, a
E       AssertionError: This is JSON
E         {
E           'foo': 'bar'
E         }
E       assert 1 == 2
E        +  where 1 = This is JSON\n{\n  'foo': 'bar'\n}.a

failure_demo.py:261: AssertionError
============================= warnings summary =============================
<undetermined location>
  Metafunc.addcall is deprecated and scheduled to be removed in pytest 4.0.
  Please use Metafunc.parametrize instead.

-- Docs: http://doc.pytest.org/en/latest/warnings.html
================== 42 failed, 1 warnings in 0.12 seconds ===================