When you want to print to standard output with print while testing with pytest

From the conclusion, adding the -s option is OK

When testing with pytest, there are times when you want to check not only the result but also the value of a variable in the middle. In conclusion, it will be output if you add the -s option.

$ pytest -s

Example 1 without -s

Consider the following code.

test_one.py


# test_one.py
def test_good():
    for i in range(5):
        print(i)
    assert True


def test_bad():
    print('this should fail!')
    assert False

When tested without the -s option, there is no output inside the loop.

$ pytest
=========================================================== test session starts ===========================================================
platform darwin -- Python 3.7.0, pytest-6.2.1, py-1.10.0, pluggy-0.13.1
rootdir: /Users/reishimitani/Desktop/d2xx/D2XX
collected 2 items

test_one.py .F                                                                                                                      [100%]

================================================================ FAILURES =================================================================
________________________________________________________________ test_bad _________________________________________________________________

    def test_bad():
        print('this should fail!')
>       assert False
E       assert False

test_one.py:10: AssertionError
---------------------------------------------------------- Captured stdout call -----------------------------------------------------------
this should fail!
========================================================= short test summary info =========================================================
FAILED test_one.py::test_bad - assert False
======================================================= 1 failed, 1 passed in 0.37s =======================================================

Example 2 When using -s

Try adding -s with the same code. The output inside the loop is output.

$ pytest -s
=========================================================== test session starts ===========================================================
platform darwin -- Python 3.7.0, pytest-6.2.1, py-1.10.0, pluggy-0.13.1
rootdir: /Users/reishimitani/Desktop/d2xx/D2XX
collected 2 items

test_one.py 0
1
2
3
4
.this should fail!
F

================================================================ FAILURES =================================================================
________________________________________________________________ test_bad _________________________________________________________________

    def test_bad():
        print('this should fail!')
>       assert False
E       assert False

test_one.py:10: AssertionError
========================================================= short test summary info =========================================================
FAILED test_one.py::test_bad - assert False
======================================================= 1 failed, 1 passed in 0.34s =======================================================

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