pytest assert introspection in helper function

Question

pytest does wonderful assert introspection so it is easy to find differences in strings especially if the difference is in white space. Now I use a slightly complicated test helper that I reuse in many testcases. The helper has its own module, too and for that module I want to add assert introspection.

helpers.py:

... def my_helper():     assert 'abcy' == 'abcx' 

test_mycase.py:

from .helpers import my_helper   def test_assert_in_tc():     assert 'abcy' == 'abcx'   def test_assert_in_helper():     my_helper() 

test report shows helpful information for asserts within tests but not for asserts within the helper:

=============================================================== FAILURES ================================================================ ___________________________________________________________ test_assert_in_tc ___________________________________________________________      def test_assert_in_tc(): >       assert 'abcy' == 'abcx' E       assert 'abcy' == 'abcx' E         - abcy E         ?    ^ E         + abcx E         ?    ^  tests/test_pytest_assert.py:9: AssertionError _________________________________________________________ test_assert_in_helper _________________________________________________________      def test_assert_in_helper(): >       my_helper()  tests/test_pytest_assert.py:13:  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _      def my_helper(): >       assert 'abcy' == 'abcx' E       AssertionError  tests/helpers.py:258: AssertionError ======================================================= 2 failed in 0.24 seconds ======================================================== 

As a workaround I output additional info with the assert but the output still looks weird and makes the code blow up. Any ideas how I can activate pytest assert introspection within the helper file?

I found a different, but related question unfortunately I could not get the solution working so far:

import pytest from .helpers import my_helper pytest.register_assert_rewrite('helpers.my_helper') 

Answer 1

I had to put the register_assert_rewrite into tests/__init__.py like so:

import pytest  # we want to have pytest assert introspection in the helpers pytest.register_assert_rewrite('tests.helpers')