【pytest】pytest断言技巧

image1

pytest的断言把Python语言简洁的优点发挥的淋漓尽致,因为它用的就是Python的标准断言assert

assert基础

assert用法

assert_stmt ::=  "assert" expression1 ["," expression2]

“assert” expression1,expression1和 if 的条件语句是一模一样的,if 能写什么这里就能写什么。

[“,” expression2],是可选的,不写错误信息也可以。

assert断言等价于

if __debug__:
    if not expression1: raise AssertionError(expression2)

示例,只考了59分,满分100分,不及格

def test():
    assert 59 == 100, "不及格"

结果,>指出了断言失败的代码行,E指出了具体的错误

a.py::test FAILED                                                        [100%]
AssertionError: 不及格
59 != 100

Expected :100
Actual   :59
<Click to see difference>

def test():
>       assert 59 == 100, "不及格"
E       AssertionError: 不及格
E       assert 59 == 100

a.py:2: AssertionError


================================== FAILURES ===================================
____________________________________ test _____________________________________

    def test():
>       assert 59 == 100, "不及格"
E       AssertionError: 不及格
E       assert 59 == 100

a.py:2: AssertionError
=========================== short test summary info ===========================
FAILED a.py::test - AssertionError: 不及格
============================== 1 failed in 0.30s ==============================

把这个例子稍微抽象一下,assert 实际 == 预期,错误信息。记住把预期放在右边

pytest.raises

pytest.raises用于断言异常。

示例,断言会抛出ZeroDivisionError,如果抛出了测试结果是pass,如果没抛出,测试结果是failed

import pytest

def test_zero_division():
    with pytest.raises(ZeroDivisionError):
        1 / 0

同时可以断言异常信息。示例,定义f(),递归循环抛异常,assert断言这个异常信息包括“maximum recursion”

def test_recursion_depth():
    with pytest.raises(RuntimeError) as excinfo:

        def f():
            f()

        f()
    assert "maximum recursion" in str(excinfo.value)

可以添加match参数来用正则过滤异常信息。示例,匹配包括123的异常

import pytest

def myfunc():
    raise ValueError("Exception 123 raised")


def test_match():
    with pytest.raises(ValueError, match=r".* 123 .*"):
        myfunc()

如果是对整个test异常断言,也可以加marker xfail

@pytest.mark.xfail(raises=IndexError)

44个failure例子

每个test用大横线做了分隔

assertion $ pytest failure_demo.py
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-6.x.y, py-1.x.y, pluggy-0.x.y
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR/assertion
collected 44 items
failure_demo.py FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF [100%]


================================= FAILURES =================================
___________________________ test_generative[3-6] ___________________________
param1 = 3, param2 = 6
    @pytest.mark.parametrize("param1, param2", [(3, 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:30: 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:33:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
a = 42, b = 54
    def otherfunc_multi(a, b):
>       assert a == b
E       assert 42 == 54
failure_demo.py:14: 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:39: 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         - eggs
E         + spam
failure_demo.py:44: 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 2 bar
E         ? ^
E         + foo 1 bar
E         ? ^
failure_demo.py:47: 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         - eggs
E         + spam
E         bar
failure_demo.py:50: 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' == '111111111111...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         - 1111111111b222222222
E         ? ^
E         + 1111111111a222222222
E         ? ^
failure_demo.py:55: 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\n...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:60: 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:63: 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:68: 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 1 more item:
E         {'c': 0}
E         Right contains 1 more item:
E         {'d': 0}...
E
E         ...Full output truncated (2 lines hidden), use '-vv' to show
failure_demo.py:71: 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:74: 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 one more item: 3
E         Use -v to get the full diff
failure_demo.py:77: 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:80: 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 multil...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:84: 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:88: 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 h...l 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:92: 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 h...ltail 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:96: AssertionError


______________ TestSpecialisedExplanations.test_eq_dataclass _______________
self = <failure_demo.TestSpecialisedExplanations object at 0xdeadbeef>
    def test_eq_dataclass(self):
        from dataclasses import dataclass
        @dataclass
        class Foo:
            a: int
            b: str
        left = Foo(1, "b")
        right = Foo(1, "c")
>       assert left == right
E       AssertionError: assert TestSpecialis...oo(a=1, b='b') == TestSpecialis...oo(a=1, b='c')
E
E       Omitting 1 identical items, use -vv to show
E       Differing attributes:
E       ['b']
E
E       Drill down into differing attribute b:
E         b: 'b' != 'c'...
E
E       ...Full output truncated (3 lines hidden), use '-vv' to show
failure_demo.py:108: AssertionError


________________ TestSpecialisedExplanations.test_eq_attrs _________________
self = <failure_demo.TestSpecialisedExplanations object at 0xdeadbeef>
    def test_eq_attrs(self):
        import attr
        @attr.s
        class Foo:
            a = attr.ib()
            b = attr.ib()
        left = Foo(1, "b")
        right = Foo(1, "c")
>       assert left == right
E       AssertionError: assert Foo(a=1, b='b') == Foo(a=1, b='c')
E
E         Omitting 1 identical items, use -vv to show
E         Differing attributes:
E         ['b']
E
E         Drill down into differing attribute b:
E           b: 'b' != 'c'...
E
E         ...Full output truncated (3 lines hidden), use '-vv' to show
failure_demo.py:120: AssertionError


______________________________ test_attribute ______________________________
    def test_attribute():
        class Foo:
            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:128: AssertionError


_________________________ test_attribute_instance __________________________
    def test_attribute_instance():
        class Foo:
            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:135: AssertionError


__________________________ test_attribute_failure __________________________
    def test_attribute_failure():
        class Foo:
            def _get_b(self):
                raise Exception("Failed to get attrib")
            b = property(_get_b)
        i = Foo()
>       assert i.b == 2
failure_demo.py:146:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
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:141: Exception


_________________________ test_attribute_multiple __________________________
def test_attribute_multiple():
    class Foo:
        b = 1
    class Bar:
        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:156: AssertionError


__________________________ TestRaises.test_raises __________________________
self = <failure_demo.TestRaises object at 0xdeadbeef>
    def test_raises(self):
        s = "qwe"
>       raises(TypeError, int, s)
E       ValueError: invalid literal for int() with base 10: 'qwe'
failure_demo.py:166: ValueError


______________________ TestRaises.test_raises_doesnt _______________________
self = <failure_demo.TestRaises object at 0xdeadbeef>
    def test_raises_doesnt(self):
>       raises(OSError, int, "3")
E       Failed: DID NOT RAISE <class 'OSError'>
failure_demo.py:169: 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:172: 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:175: 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}".format(items))
>       a, b = items.pop()
E       TypeError: cannot unpack non-iterable int object
failure_demo.py:180: 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:183: NameError


____________________ test_dynamic_compile_shows_nicely _____________________
    def test_dynamic_compile_shows_nicely():
        import importlib.util
        import sys
        src = "def foo():\n assert 1 == 0\n"
        name = "abc-123"
        spec = importlib.util.spec_from_loader(name, loader=None)
        module = importlib.util.module_from_spec(spec)
        code = compile(src, name, "exec")
        exec(code, module.__dict__)
        sys.modules[name] = module
>       module.foo()
failure_demo.py:202:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
>   ???
E   AssertionError
abc-123:2: 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:213:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
failure_demo.py:10: in somefunc
    otherfunc(x, y)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
a = 44, b = 43
    def otherfunc(a, b):
>       assert a == b
E       assert 44 == 43
failure_demo.py:6: 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:217: 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: cannot unpack non-iterable int object
failure_demo.py:221: 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:226: 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:235: 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:238: 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:242: 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:245: 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:250: AssertionError


___________________ TestCustomAssertMsg.test_single_line ___________________
self = <failure_demo.TestCustomAssertMsg object at 0xdeadbeef>
    def test_single_line(self):
        class A:
            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:261: AssertionError


____________________ TestCustomAssertMsg.test_multiline ____________________
self = <failure_demo.TestCustomAssertMsg object at 0xdeadbeef>
    def test_multiline(self):
        class A:
            a = 1
        b = 2
>       assert (
            A.a == b
        ), "A.a appears not to be b\nor 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:268: AssertionError


___________________ TestCustomAssertMsg.test_custom_repr ___________________
self = <failure_demo.TestCustomAssertMsg object at 0xdeadbeef>
    def test_custom_repr(self):
        class JSON:
            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:281: AssertionError


============================ 44 failed in 0.12s ============================