如何使用pytest测试try/except块的异常

Question

在 try/except 块中触发异常后，如何正确测试是否执行了正确的代码？

import pytest


def my_func(string):
    try:
        assert string == "pass"
        print("String is `pass`")
    except AssertionError:
        print("String is not 'pass'")



def test_my_func():
    with pytest.raises(AssertionError) as exc_info:
        my_func("fail")

    assert str(exc_info.value) == "String is not 'pass'"

很明显，这个测试失败了 Failed: DID NOT RAISE <class 'AssertionError'>，因为我在 try/except 块中发现了错误。但是 can/should 我如何测试是否打印了正确的短语？如果您有多个可能的 except 块，这可能特别有用。

Answer 1

您可以使用 capsys fixture 捕获标准输出，然后用它进行断言：

def my_func(string):
    try:
        assert string == "pass"
        print("String is `pass`")
    except AssertionError:
        print("String is not 'pass'")



def test_my_func(capsys):
    my_func("fail")
    captured = capsys.readouterr()
    assert captured.out == "String is not 'pass'\n"

如何使用pytest测试try/except块的异常

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