pytest_cs.py

###### Pytest fixtures

# Basic toy example:
import pytest

@pytest.fixture()
def before():
    print('\nbefore each test')
 
def test_1(before):
    print('test_1()')

def test_2(before):
    print('test_2()')

# Fixture return a dict:
import pytest

@pytest.fixture()
def some_data():
    data = {'foo':1, 'bar':2, 'baz':3}
    return data

def test_foo(some_data):
    assert some_data['foo'] == 1

# Scope a fixture

# 'function' is the default scope and means that the the fixture will be executed before each test
import pytest

@pytest.fixture(scope="function")
def before():
    print('before each test')
 
def test_1(before):
    print('test_1()')

def test_2(before):
    print('test_2()')

## 'module' . Fixture will be executed only once
import pytest

@pytest.fixture(scope="module")
def before():
    print('before each test')
 
def test_1(before):
    print('test_1()')

def test_2(before):
    print('test_2()')

## teardown code
@pytest.fixture()
def cheese_db(request):
    print('\n[setup] cheese_db, connect to db')
    # code to connect to your db 
    a_dictionary_for_now = {'Brie': 'No.', 'Camenbert': 'Ah! We have Camenbert, yessir.'}
    def fin():
        print('\n[teardown] cheese_db finalizer, disconnect from db')
    request.addfinalizer(fin)
    return a_dictionary_for_now

def test_cheese_database(cheese_db):
    print('in test_cheese_database()')
    for variety in cheese_db.keys():
        print('%s : %s' % (variety, cheese_db[variety]))

def test_brie(cheese_db):
    print('in test_brie()')
    assert cheese_db['Brie'] == 'No.' 

def test_camenbert(cheese_db):
    print('in test_camenbert()')
    assert cheese_db['Camenbert'] != 'No.' 

## Fixture to generate a set of params:
import pytest

@pytest.fixture( params=[1,2,3] )
def test_data(request):
    return request.param

def test_not_2(test_data):
    print('test_data: %s' % test_data)
    assert test_data != 2

## How to share the smae fixtures among different test files

1) Include the fixtures you want to share in a file named conftest.py 
that will be placed in the test root folder. Ex:
import pytest

@pytest.fixture(scope="session")
def before():
    print('before each test')
    return 'a'
 
@pytest.fixture(scope="session")
def after():
    print('after each test')
    return 'b'
  
2) Then, write a test file named test_pytest.py that will use the fixtures in conftest.py:
import pytest
 
def test_1(before):
    print('test_1()')
    print(f"Returned: {before}")

def test_2(after):
    print('test_1()')
    print(f"Returned: {after}")
3) Execute:
$ pytest -s -v test_pytest.py 
You will get:
collected 2 items                                                                                                                                                                                                                                                                                                                                              

test_pytest.py::test_1 before each test
test_1()
Returned: a
PASSED
test_pytest.py::test_2 after each test
test_1()
Returned: b
PASSED


###### How to do a pytest with multiple params:

# 1) Containing only 2 params:
# content of test_expectation.py
import pytest

@pytest.mark.parametrize("test_input,expected", [("3+5", 8), ("2+4", 6), ("6*9", 42)])
def test_eval(test_input, expected):
    assert eval(test_input) == expected
# 2) Containing 3 params:
# content of test_expectation.py
import pytest

@pytest.mark.parametrize("a,b,expected", [(1,2,3), (2,4,6), (3,10,42)])
def test_eval(a,b,expected):
    assert a+b == expected

//
# Selecting specific tests to run
pytest test_file.py -k 'test_one or test_two'

#####Setting env (environment) variables for the tests.
# conftest.py
import pytest

@pytest.fixture(autouse=True) # make sure that this is executed in each test
def env_setup(monkeypatch):
    monkeypatch.setenv('TEST', 'foo')
    
# Now, we have the file that uses the fixture
# test_1.py
import pytest
import os

def test_1():
    print(os.environ['TEST'])
    assert 1 == 1

# check if a file has been created by a test
assert os.path.exists(outfile) == 1