Python pytest：捕获标准输出总是失败答案

【问题标题】：Python pytest: capturing stdout always failsPython pytest：捕获标准输出总是失败
【发布时间】：2017-09-13 15:50:46
【问题描述】：

我正在尝试在 pytest 中捕获 stdout / print 语句的输出（Python 3.6 版）。

这总是失败：

message = 'The meaning of life is not actually 42\n'

def print_greeting():
    """print 42 to stdout"""

    # write to stdout
    sys.stdout.write(message)           # this fails

    # print to stdout
    print('Message again: ', message)   # this fails too


def test_printgreeting(capsys):
    """assert '42' was printed to stdout"""

    # capture stdout / stderr
    out, err = capsys.readouterr()
    print_greeting()

    # 42 should be in stdout from sys.stdout.write
    assert '42' in out

pytest 的结果：

========================================================= test session starts ==========================================================

collected 1 item

test.py
The meaning of life is not actually 42
F

=============================================================== FAILURES ===============================================================
__________________________________________________________ test_printgreeting __________________________________________________________
test.py:42: in test_printgreeting
    assert '42' in out
E   AssertionError: assert '42' in ''
======================================================= 1 failed in 0.03 seconds =======================================================

为什么没有捕获？

【问题讨论】：

标签： python unit-testing tdd pytest

【解决方案1】：

您需要在打印后致电readouterr：

def test_printgreeting(capsys):
    """assert '42' was printed to stdout"""

    # capture stdout / stderr
    print_greeting()
    out, err = capsys.readouterr()

    # 42 should be in stdout from sys.stdout.write
    assert '42' in out

【讨论】：

天哪。我用头敲了三个小时。 >,
非常感谢。