Pytest框架 — 04、Pytest的断言

1、前言

Pytest使用python自带关键字assert进行断言,断言内容为一个表达式,只要表达式的最终结果为True,那么断言通过,用例执行成功,否则用例执行失败。
assert + 表达式

2、常用断言

  • assert xx:判断xx为真
  • assert not xx: 判断xx不为真
  • assert a in b:判断b包含a
  • assert a == b: 判断a等于b
  • assert a != b: 判断a不等于b

3、预期异常断言

除了支持对代码正常运行的结果断言之外,Pytest也能够对 Exception 和 Warnning 进行断言。有时候断言会引发我们意料之中的异常,借助pytest.raises可以捕获匹配到的异常,避免该条用例执行Failed。

  • 示例1:如果抛出ZeroDivisionError测试结果是Pass,否则为Failed
def test_zero():
    # 捕获预期异常
    with pytest.raises(ZeroDivisionError) as ec:
        res = 1 / 0
    # 断言异常信息, 官方提示, raise 的异常应该是当前代码块最后一行,如果在其后面还有代码,那么将不会被执行。
    assert "zero" in str(ec.value)
  • 示例2:将异常信息存储到一个变量中,从而可以进一步断言
def test_zero():
    # 捕获预期异常
    with pytest.raises(ValueError) as ec:
        raise ValueError("Zero Error")
	# 官方提示, raise 的异常应该是当前代码块最后一行,如果在其后面还有代码,那么将不会被执行。
    print("错误说明", ec.value)
    print("错误回溯", ec.traceback)
    print("错误类型",ec.type)
    assert str(ec.value) == "Zero Error"

"""
执行结果
collected 1 item                                                                                                                              

test_temp.py::test_zero 错误说明 Zero Error
错误回溯 [<TracebackEntry /Users/qishuai/Desktop/笔记/web自动化测试/pytest/demo/test_temp.py:30>]
错误类型 <class 'ValueError'>
PASSED

"""
  • 示例3:预期异常还可以传递一个元祖
def test_Error_tuple():
   with pytest.raises((ValueError, ZeroDivisionError)):
       # res = 1/0
       raise ValueError
  • 示例4:通过match关键字进行正则表达式更精确断言异常
def match_error():
    raise ValueError("This is Test Error")

def match_error_2():
    raise ValueError

def test_match():
    with pytest.raises(ValueError,match=r".* Test Error") as ec:
        match_error_2()
    assert ec.type == ValueError
    assert str(ec.value) == "This is Test Error"

上面示例4代码中由于添加了match关键字,所以match_error引发的异常能被pytest.raise捕获到,match_error_2引发的异常不能被pytest.raise捕获到。

更多异常断言:https://docs.pytest.org/en/latest/how-to/assert.html#assertions-about-expected-exceptions

4、优化断言提示

在断言时加入注释字符串,在报错时注释能够被打印出来

def test_assert_fail():
    assert 1 > 2, "断言1是否大于2"

"""
执行结果
============================ test session starts ==============================
collecting ... collected 1 item

test_1.py::test_assert_fail FAILED                                       [100%]
test_1.py:41 (test_assert_fail)
def test_assert_fail():
>       assert 1 > 2, "断言1是否大于2"
E       AssertionError: 断言1是否大于2
E       assert 1 > 2

test_1.py:43: AssertionError


============================== 1 failed in 0.06s ===============================
"""

5、自定义失败断言提示

通过在conftest.py中添加pytest_assertrepr_compare钩子来添加您自己的详细解释,如下:

# content of conftest.py
def pytest_assertrepr_compare(op, left, right):
    """
    :param op: 操作符
    :param left: 操作符左边内容
    :param right: 操作符右边内容
    :return: 
    """
    if op == ">":
        return ["比较大小",f"{left}不大于{right}"]
# content of test_compare.py
def test_compare():
    a = 1
    b = 2
    assert a > b
"""
执行结果:
collected 1 item                                                                                                                              

temp/test_compare_foo.py::test_compare FAILED

================================================================== FAILURES ===================================================================
________________________________________________________________ test_compare _________________________________________________________________

    def test_compare():
        a = 1
        b = 2
>       assert a > b
E       assert 比较大小
E         1不大于2

temp/test_compare_foo.py:19: AssertionError
=========================================================== short test summary info ===========================================================
FAILED temp/test_compare_foo.py::test_compare - assert 比较大小
============================================================== 1 failed in 0.08s ==============================================================
"""

参考:
https://cloud.tencent.com/developer/article/1693769
http://www.360doc.com/content/22/0211/10/78594709_1016826734.shtml
https://docs.pytest.org/en/latest/how-to/assert.html#assertions-about-expected-exceptions

posted @ 2022-08-10 19:04  睡觉大王Risen  阅读(476)  评论(0编辑  收藏  举报