iOS自动化探索（五）自动化测试框架pytest - Assert断言的使用

使用assert语句进行断言

pytest允许使用标准的python assert语法，用来校验expectation and value是否一致

代码演示:

def func():
    return 

def test_func():
    assert func() ==
    

执行结果:

(wda_python) bash-3.2$ pytest -q test_assert.py
F                                                                                                                                  [%]
================================================================ FAILURES ================================================================
_______________________________________________________________ test_func ________________________________________________________________

    def test_func():
>       assert func() ==
E       assert  ==
E        +  where  = func()

test_assert.py:: AssertionError
 failed in 0.07 seconds
(wda_python) bash-3.2$ 

同时支持在assert后面添加描述信息:

def func():
    return 

def test_func():
    assert func() == , 'Value was odd, should be even'

执行结果：

(wda_python) bash-3.2$ pytest -q test_assert.py
F                                                                                                                                  [%]
================================================================ FAILURES ================================================================
_______________________________________________________________ test_func ________________________________________________________________

    def test_func():
>       assert func() == , 'Value was odd, should be even'
E       AssertionError: Value was odd, should be even
E       assert  ==
E        +  where  = func()

test_assert.py:: AssertionError
 failed in 0.07 seconds
(wda_python) bash-3.2$ 

预期异常的断言

pytest中使用with pytest.raises: 来断言预期异常

代码演示:

import pytest

def func():
    raise SystemExit(1)

def test_func():
    with pytest.raises(SystemExit):
        func()

执行输出：

(wda_python) bash-3.2$ pytest -q test_sysexit.py
.                                                                                                                                      [%]
 passed in 0.04 seconds
(wda_python) bash-3.2$ 

还可以自定义错误描述:

import pytest

def func():
    raise SystemError("Exception 123 raised")

def test_func():
    with pytest.raises(SystemError, match=r'.* 123 .*'):
        func()

输出:

(wda_python) bash-3.2$ pytest -q test_assert.py
.                                                                                                                                  [%]
 passed in 0.03 seconds
(wda_python) bash-3.2$ 

如果不匹配的话就会报错:

import pytest

def func():
    raise SystemError("Exception 12 raised")

def test_func():
    with pytest.raises(SystemError, match=r'.* 123 .*'):
        func()

输出:

(wda_python) bash-3.2$ pytest -q test_assert.py
F                                                                                                                                  [%]
================================================================ FAILURES ================================================================
_______________________________________________________________ test_func ________________________________________________________________

    def test_func():
        with pytest.raises(SystemError, match=r'.* 123 .*'):
>           func()
E           AssertionError: Pattern '.* 123 .*' not found in 'Exception 124 raised'

test_assert.py:: AssertionError
 failed in 0.07 seconds
(wda_python) bash-3.2$ 

断言上下文内容(变量)是否相等

实例代码:

def test_set_comparison():
    set1 = set('')
    set2 = set('')
    assert set1 == set2

运行结果:

(wda_python) bash-3.2$ pytest -q test_assert.py
F                                                                                                                                  [%]
================================================================ FAILURES ================================================================
__________________________________________________________ test_set_comparison ___________________________________________________________

    def test_set_comparison():
        set1 = set('')
        set2 = set('')
>       assert set1 == set2
E       AssertionError: assert set(['', '', '', '']) == set(['', '', '', ''])
E         Extra items in the left set:
E         ''
E         Extra items in the right set:
E         ''
E         Full diff:
E         - set(['', '', '', ''])
E         ?           -----...
E
E         ...Full output truncated ( lines hidden), use '-vv' to show

test_assert.py:: AssertionError
 failed in 0.10 seconds
(wda_python) bash-3.2$ 

自定义断言

官方解释如下

 

我们可以通过实现pytest_assertrepr_compare方法，来自定义assert实现

比如一个Class Foo，我们比较f1和f2

class Foo(object):
    def __init__(self, val):
        self.val = val

    def __eq__(self, other):
        return self.val == other.val

def test_compare():
    f1 = Foo()
    f2 = Foo(1)
    assert f1 == f2

运行结果如下:

(wda_python) bash-3.2$ pytest -q test_foocompare.py
F                                                                                                                                  [%]
================================================================ FAILURES ================================================================
______________________________________________________________ test_compare ______________________________________________________________

    def test_compare():
        f1 = Foo()
        f2 = Foo()
>       assert f1 == f2
E       assert <test_foocompare.Foo object at 0x1029eb7d0> == <test_foocompare.Foo object at 0x1029eb290>

test_foocompare.py:: AssertionError
 failed in 0.09 seconds
(wda_python) bash-3.2$ 

错误提示不够友好， 我们可以通过完成pytest_assertrepr_compare方法自定义

from test_foocompare import Foo

def pytest_assertrepr_compare(op, left, right):
    if isinstance(left, Foo) and isinstance(right, Foo) and op == "==":
        return ['Comparing Foo instance:', 'vals: %s != %s' % (left.val, right.val)]

运行结果如下:

(wda_python) bash-3.2$ pytest
========================================================== test session starts ===========================================================
platform darwin -- Python 2.7., pytest-4.1., py-1.7., pluggy-0.8.
rootdir: /Users/jackey/Documents/iOS/code/iOS-Auto/Agent_Test, inifile:
collected  item                                                                                                                         

test_foocompare.py F                                                                                                               [%]

================================================================ FAILURES ================================================================
______________________________________________________________ test_compare ______________________________________________________________

    def test_compare():
        f1 = Foo()
        f2 = Foo()
>       assert f1 == f2
E       assert Comparing Foo instance:
E         vals:  != 

test_foocompare.py:: AssertionError
========================================================  failed in 0.05 seconds ========================================================
(wda_python) bash-3.2$