pytest "cannot collect test class because it has a __init__" in CI

pytest instantiates test classes itself and cannot do so if the class defines __init__. It emits a collection warning and skips the class, so its tests silently do not run - a real risk when the suite is supposed to be green.

What this error means

pytest prints "PytestCollectionWarning: cannot collect test class 'TestX' because it has a __init__ constructor" and the class's tests are not executed.

tests/test_service.py:5
  PytestCollectionWarning: cannot collect test class 'TestService' because it has a
  __init__ constructor (from: tests/test_service.py)

Common causes

A test class defines __init__

pytest needs to construct the class with no arguments; an __init__ prevents that, so collection is skipped.

A non-test class matched the Test* pattern

A helper class named TestSomething is picked up by collection but has a constructor, triggering the warning.

How to fix it

Use fixtures instead of __init__

Move per-test setup into a fixture or setup_method so the class needs no constructor.

class TestService:
    @pytest.fixture(autouse=True)
    def setup(self):
        self.svc = Service()

Rename non-test helper classes

If the class is not a test, rename it so it does not match the Test* collection pattern.

class ServiceHarness:  # not collected
    def __init__(self):
        ...

How to prevent it

• Do not give test classes an __init__; use fixtures or setup_method.
• Name non-test helpers so they do not match Test*.
• Treat collection warnings as errors to catch silently-skipped tests.

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