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Pytestで標準出力をテストする

Posted at

業務でPythonを使うことになり、標準出力をテストしたかったのでメモとして

準備

  • Python 3系
  • pytest
pip install pytest

テスト対象コード

下記プログラムをテストしたいと思います。
sayメソッドで標準出力へ出すだけです。

hogehoge.py
class HogeHoge:
  def __init__(self, name):
    self.name = name
  
  def say(self):
    print("Hello ! My name is " + self.name + ".")

テストコード

pytestにある fixture、capfdを使う

test_hogehoge.py
from hogehoge import HogeHoge

def test_say(capfd):
  instance = HogeHoge("Taro")
  instance.say()

  out, err = capfd.readouterr()
  assert out == "Hello ! My name is Taro.\n"
  assert err is ''
[Sun Nov 24 17:58:49 2019] Running: c:\python\python.exe -m pytest
============================== test session starts =============================== 
platform win32 -- Python 3.7.2, pytest-5.3.0, py-1.8.0, pluggy-0.13.1
rootdir: D:\Document\repository\study_pytest
collected 1 item

test\test_hogehoge.py .                                                     [100%] 

=============================== 1 passed in 0.08s ================================ 

まとめ

標準出力のテストには、capfdを使おう。標準エラーも取得できます。

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