使用assert語句進行斷言

pytest允許使用標準的python assert語法，用來校驗expectation and value是否一致

程式碼演示:

def func():
    return 3

def test_func():
    assert func() == 4
    

執行結果:

(wda_python) bash-3.2$ pytest -q test_assert.py 
F                                                                                                                                  [
 
100%]
================================================================ FAILURES ================================================================
_______________________________________________________________ test_func ________________________________________________________________

    def test_func():
 
>       assert func() == 4
E       assert 3 == 4
E        +  where 3 = func()

test_assert.py:5: AssertionError
1 failed in 0.07 seconds
(wda_python) bash-3.2$ 

 

同時支援在assert後面新增描述資訊:

def func():
    return 3

def test_func():
    assert func() == 4, 'Value was odd, should be even
 
'

執行結果：

(wda_python) bash-3.2$ pytest -q test_assert.py 
F                                                                                                                                  [100%]
================================================================ FAILURES ================================================================
_______________________________________________________________ test_func ________________________________________________________________

    def test_func():
>       assert func() == 4, 'Value was odd, should be even'
E       AssertionError: Value was odd, should be even
E       assert 3 == 4
E        +  where 3 = func()

test_assert.py:5: AssertionError
1 failed in 0.07 seconds
(wda_python) bash-3.2$ 

 

預期異常的斷言

pytest中使用with pytest.raises: 來斷言預期異常

程式碼演示:

import pytest

def func():
    raise SystemExit(1)

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

執行輸出：

(wda_python) bash-3.2$ pytest -q test_sysexit.py 
.                                                                                                                                      [100%]
1 passed in 0.04 seconds
(wda_python) bash-3.2$ 

 

還可以自定義錯誤描述:

import pytest

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

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

輸出:

(wda_python) bash-3.2$ pytest -q test_assert.py 
.                                                                                                                                  [100%]
1 passed in 0.03 seconds
(wda_python) bash-3.2$ 

如果不匹配的話就會報錯:

import pytest

def func():
    raise SystemError("Exception 124 raised")

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

輸出:

(wda_python) bash-3.2$ pytest -q test_assert.py 
F                                                                                                                                  [100%]
================================================================ 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:8: AssertionError
1 failed in 0.07 seconds
(wda_python) bash-3.2$ 

 

斷言上下文內容(變數)是否相等

例項程式碼:

def test_set_comparison():
    set1 = set('1308')
    set2 = set('8035')
    assert set1 == set2

執行結果:

(wda_python) bash-3.2$ pytest -q test_assert.py 
F                                                                                                                                  [100%]
================================================================ FAILURES ================================================================
__________________________________________________________ test_set_comparison ___________________________________________________________

    def test_set_comparison():
        set1 = set('1308')
        set2 = set('8035')
>       assert set1 == set2
E       AssertionError: assert set(['0', '1', '3', '8']) == set(['0', '3', '5', '8'])
E         Extra items in the left set:
E         '1'
E         Extra items in the right set:
E         '5'
E         Full diff:
E         - set(['0', '1', '3', '8'])
E         ?           -----...
E         
E         ...Full output truncated (3 lines hidden), use '-vv' to show

test_assert.py:4: AssertionError
1 failed in 0.10 seconds
(wda_python) bash-3.2$ 

 

自定義斷言

官方解釋如下

 

我們可以通過實現pytest_assertrepr_compare方法，來自定義assert實現

比如一個Class Foo，我們比較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(1)
    f2 = Foo(1)
    assert f1 == f2

執行結果如下:

(wda_python) bash-3.2$ pytest -q test_foocompare.py 
F                                                                                                                                  [100%]
================================================================ FAILURES ================================================================
______________________________________________________________ test_compare ______________________________________________________________

    def test_compare():
        f1 = Foo(1)
        f2 = Foo(2)
>       assert f1 == f2
E       assert <test_foocompare.Foo object at 0x1029eb7d0> == <test_foocompare.Foo object at 0x1029eb290>

test_foocompare.py:11: AssertionError
1 failed in 0.09 seconds
(wda_python) bash-3.2$ 

錯誤提示不夠友好， 我們可以通過完成pytest_assertrepr_compare方法自定義

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)]

執行結果如下:

(wda_python) bash-3.2$ pytest
========================================================== test session starts ===========================================================
platform darwin -- Python 2.7.15, pytest-4.1.0, py-1.7.0, pluggy-0.8.0
rootdir: /Users/jackey/Documents/iOS/code/iOS-Auto/Agent_Test, inifile:
collected 1 item                                                                                                                         

test_foocompare.py F                                                                                                               [100%]

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

    def test_compare():
        f1 = Foo(1)
        f2 = Foo(2)
>       assert f1 == f2
E       assert Comparing Foo instance:
E         vals: 1 != 2

test_foocompare.py:11: AssertionError
======================================================== 1 failed in 0.05 seconds ========================================================
(wda_python) bash-3.2$