Python pytest：捕获标准输出总是失败

Question

我正在尝试从 pytest（Python 版本 3.6）中的标准输出/打印语句捕获输出。

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 =======================================================

为什么没有捕获到这个？

Answer 1

您需要在打印后调用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

Python pytest：捕获标准输出总是失败

Python pytest: capturing stdout always fails

python

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unit-testing

pytest