How can I get pytest to not catch exceptions

user_389806 0
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When I run pytest in the vscode debugger with "Uncaught Exceptions" checked, and there are test errors, no uncaught exceptions occur, because pytest catches them do its results reporting. How can I tell pytest to just let the exceptions happen? So that I can catch them in the vscode debugger?

Basically I want behavior like --pdb but I want it to launch the vscode debugger not pdb. The flag --pdbcls sounds promising but not sure what <module>:<class> to give it.

Note: Normally I would just have it break on Raised Exceptions. But our code has tons of raised-but-caught exceptions so this option is not useful.

Here's a video of vscode not breaking when an AssertionError fires while debugging a pytest test:

enter image description here

@rioV8's suggestion below does break the on the exception, but for some reason there is no stack which means you can't debug from there:

enter image description here

I must be missing something because no one else seems to need this capability. But to me this seems like absolutely the most basic simplest thing one could do with a testing framework and a debugger: as a developer I want to debug from the point where the error is raised.

There must be some totally other way people are using a debugger with pytest, some obvious technique I'm overlooking.

vscode-python vscode-debugger visual-studio-code
3 Answers

I raised an issue with pytest and they made a suggestion that works. Add this to your conftest.py:

import os
import pytest

if os.getenv('_PYTEST_RAISE', "0") != "0":

    @pytest.hookimpl(tryfirst=True)
    def pytest_exception_interact(call):
        raise call.excinfo.value

    @pytest.hookimpl(tryfirst=True)
    def pytest_internalerror(excinfo):
        raise excinfo.value

Then in your "request": "test" launch.json you can toggle that env var:

    {
        "name": "Debug Tests",
        "type": "python",
        "request": "test",
        "console": "integratedTerminal",
        "justMyCode": true,
        "env": {
            "_PYTEST_RAISE": "1"
        },
    }

If _PYTEST_RAISE is set and you check only the Uncaught Exceptions box you will break right where the uncaught exception was raised not before.

I also opened an issue with debugpy and they had some ideas, but no solution today. The _PYTEST_RAISE trick works 100% solves this for me.

user_3898060

I've noticed a few things that might be relevant. Even though I'm not ready to dig deeper right now, I'll post them here in case they might be useful to someone.

Workaround:

A simple hack I've used is to just (temporarily) call the relevant test case directly and "Run and Debug" the file rather than using the "Debug Test Case" button:


def test_example():
    assert False


test_example()

Result:

enter image description here

Notes:

  1. The important difference in behavior correlates with specifying "request": "test" vs specifying "request": "launch" in the launch.json configuration. (There is also a difference between the two types in whether or not the justMyCode option gets applied from a global launch configuration as described here).
  2. If you have a python "request": "test" specified, then VSCode doesn't appear to let you debug the file in launch mode as I did above.
  3. In my scenario, I had a test failing because of an exception I was causing in a third-party library (my fault, of course). Breakpoints in third-party code are apparently only triggered if the "justMyCode": false option is added.

launch.json:

{
    "version": "0.2.0",
    "configurations": [
        
        {
            "name": "Python: Current File",
            "type": "python",
            "request": "launch",
            "program": "${file}",
            "console": "integratedTerminal",
            "justMyCode": false,            
        },
        // {
        //     "name": "Debug Unit Test",
        //     "type": "python",
        //     "request": "test",
        //     "console": "integratedTerminal",
        //     "justMyCode": false,
        // }        
    ]
}
user_37803890

The behavior is not identical but the test runner stops at the uncaught exception.

Add the file conftest.py to the directory with your tests.

# conftest.py
def pytest_exception_interact(node, call, report):
  print( call.excinfo.traceback[0] )
  pass

This adds a hook for any uncaught exceptions.

Place a break point at the line with pass.

Then Debug the test.

Look in the Debug console and you see the file and line number where the exception happened.

test_example.py F  File 'path\\test_example.py':4 in test_example
  assert False

And the debugger stops at the pass line.

You can make this hook function as fancy as you like.

user_99383170
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