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 ============================