@typeguard on a test breaks pytest assertion rewriting

[adamtheturtle]

Things to check first

• I have searched the existing issues and didn't find my bug already reported there

• I have checked that my bug is still present in the latest release

Typeguard version

4.3.0

Python version

3.12

What happened?

Install pytest and typeguard.
Run the following script:

# test_example.py

import pytest

def test_example() -> None:
	result = 1
	assert result == 2

pytest.main()

See output including:

    def test_example() -> None:
    	result = 1
>   	assert result == 2
E    assert 1 == 2

Now run:

# test_example.py

import pytest
from typeguard import typechecked

@typechecked
def test_example() -> None:
	result = 1
	assert result == 2

pytest.main()

See:

    def test_example() -> None:
    	result = 1
>   	assert result == 2
E    AssertionError

How can we reproduce the bug?

Run the code examples from the previous section.

[agronholm]

I don't think there's much I can do about this, apart from returning @typechecked to wrapping the underlying function again.

[adamtheturtle]

Thank you @agronholm . I am not familiar with typeguard internals, so I don't know what encouraged the change away from that.

In case it is useful, I'll point you to https://docs.pytest.org/en/stable/how-to/writing_plugins.html#assertion-rewriting and pytest.register_assert_rewrite.

[agronholm]

Thank you @agronholm . I am not familiar with typeguard internals, so I don't know what encouraged the change away from that.

1. It creates an additional stack frame for every call
2. Without AST rewriting, I cannot inject code to check assignments to annotated local variables

[agronholm]

In case it is useful, I'll point you to https://docs.pytest.org/en/stable/how-to/writing_plugins.html#assertion-rewriting and pytest.register_assert_rewrite.

It's not useful, sorry. This API is for enabling assertion rewrite outside of the collected pytest modules.

[adamtheturtle]

Thank you again for the quick and thoughtful responses.

What do you think of making those trade-offs, but potentially only when PYTEST_CURRENT_TEST is set (https://docs.pytest.org/en/latest/example/simple.html#pytest-current-test-environment-variable)?