Edit: recwarn.py
"""Record warnings during test function execution.""" import re import warnings from pprint import pformat from types import TracebackType from typing import Any from typing import Callable from typing import Generator from typing import Iterator from typing import List from typing import Optional from typing import Pattern from typing import Tuple from typing import Type from typing import TypeVar from typing import Union from _pytest.compat import final from _pytest.compat import overload from _pytest.deprecated import check_ispytest from _pytest.deprecated import WARNS_NONE_ARG from _pytest.fixtures import fixture from _pytest.outcomes import fail T = TypeVar("T") @fixture def recwarn() -> Generator["WarningsRecorder", None, None]: """Return a :class:`WarningsRecorder` instance that records all warnings emitted by test functions. See https://docs.pytest.org/en/latest/how-to/capture-warnings.html for information on warning categories. """ wrec = WarningsRecorder(_ispytest=True) with wrec: warnings.simplefilter("default") yield wrec @overload def deprecated_call( *, match: Optional[Union[str, Pattern[str]]] = ... ) -> "WarningsRecorder": ... @overload def deprecated_call( # noqa: F811 func: Callable[..., T], *args: Any, **kwargs: Any ) -> T: ... def deprecated_call( # noqa: F811 func: Optional[Callable[..., Any]] = None, *args: Any, **kwargs: Any ) -> Union["WarningsRecorder", Any]: """Assert that code produces a ``DeprecationWarning`` or ``PendingDeprecationWarning``. This function can be used as a context manager:: >>> import warnings >>> def api_call_v2(): ... warnings.warn('use v3 of this api', DeprecationWarning) ... return 200 >>> import pytest >>> with pytest.deprecated_call(): ... assert api_call_v2() == 200 It can also be used by passing a function and ``*args`` and ``**kwargs``, in which case it will ensure calling ``func(*args, **kwargs)`` produces one of the warnings types above. The return value is the return value of the function. In the context manager form you may use the keyword argument ``match`` to assert that the warning matches a text or regex. The context manager produces a list of :class:`warnings.WarningMessage` objects, one for each warning raised. """ __tracebackhide__ = True if func is not None: args = (func,) + args return warns((DeprecationWarning, PendingDeprecationWarning), *args, **kwargs) @overload def warns( expected_warning: Union[Type[Warning], Tuple[Type[Warning], ...]] = ..., *, match: Optional[Union[str, Pattern[str]]] = ..., ) -> "WarningsChecker": ... @overload def warns( # noqa: F811 expected_warning: Union[Type[Warning], Tuple[Type[Warning], ...]], func: Callable[..., T], *args: Any, **kwargs: Any, ) -> T: ... def warns( # noqa: F811 expected_warning: Union[Type[Warning], Tuple[Type[Warning], ...]] = Warning, *args: Any, match: Optional[Union[str, Pattern[str]]] = None, **kwargs: Any, ) -> Union["WarningsChecker", Any]: r"""Assert that code raises a particular class of warning. Specifically, the parameter ``expected_warning`` can be a warning class or sequence of warning classes, and the code inside the ``with`` block must issue at least one warning of that class or classes. This helper produces a list of :class:`warnings.WarningMessage` objects, one for each warning raised (regardless of whether it is an ``expected_warning`` or not). This function can be used as a context manager, which will capture all the raised warnings inside it:: >>> import pytest >>> with pytest.warns(RuntimeWarning): ... warnings.warn("my warning", RuntimeWarning) In the context manager form you may use the keyword argument ``match`` to assert that the warning matches a text or regex:: >>> with pytest.warns(UserWarning, match='must be 0 or None'): ... warnings.warn("value must be 0 or None", UserWarning) >>> with pytest.warns(UserWarning, match=r'must be \d+$'): ... warnings.warn("value must be 42", UserWarning) >>> with pytest.warns(UserWarning, match=r'must be \d+$'): ... warnings.warn("this is not here", UserWarning) Traceback (most recent call last): ... Failed: DID NOT WARN. No warnings of type ...UserWarning... were emitted... **Using with** ``pytest.mark.parametrize`` When using :ref:`pytest.mark.parametrize ref` it is possible to parametrize tests such that some runs raise a warning and others do not. This could be achieved in the same way as with exceptions, see :ref:`parametrizing_conditional_raising` for an example. """ __tracebackhide__ = True if not args: if kwargs: argnames = ", ".join(sorted(kwargs)) raise TypeError( f"Unexpected keyword arguments passed to pytest.warns: {argnames}" "\nUse context-manager form instead?" ) return WarningsChecker(expected_warning, match_expr=match, _ispytest=True) else: func = args[0] if not callable(func): raise TypeError(f"{func!r} object (type: {type(func)}) must be callable") with WarningsChecker(expected_warning, _ispytest=True): return func(*args[1:], **kwargs) class WarningsRecorder(warnings.catch_warnings): # type:ignore[type-arg] """A context manager to record raised warnings. Each recorded warning is an instance of :class:`warnings.WarningMessage`. Adapted from `warnings.catch_warnings`. .. note:: ``DeprecationWarning`` and ``PendingDeprecationWarning`` are treated differently; see :ref:`ensuring_function_triggers`. """ def __init__(self, *, _ispytest: bool = False) -> None: check_ispytest(_ispytest) # Type ignored due to the way typeshed handles warnings.catch_warnings. super().__init__(record=True) # type: ignore[call-arg] self._entered = False self._list: List[warnings.WarningMessage] = [] @property def list(self) -> List["warnings.WarningMessage"]: """The list of recorded warnings.""" return self._list def __getitem__(self, i: int) -> "warnings.WarningMessage": """Get a recorded warning by index.""" return self._list[i] def __iter__(self) -> Iterator["warnings.WarningMessage"]: """Iterate through the recorded warnings.""" return iter(self._list) def __len__(self) -> int: """The number of recorded warnings.""" return len(self._list) def pop(self, cls: Type[Warning] = Warning) -> "warnings.WarningMessage": """Pop the first recorded warning, raise exception if not exists.""" for i, w in enumerate(self._list): if issubclass(w.category, cls): return self._list.pop(i) __tracebackhide__ = True raise AssertionError(f"{cls!r} not found in warning list") def clear(self) -> None: """Clear the list of recorded warnings.""" self._list[:] = [] # Type ignored because it doesn't exactly warnings.catch_warnings.__enter__ # -- it returns a List but we only emulate one. def __enter__(self) -> "WarningsRecorder": # type: ignore if self._entered: __tracebackhide__ = True raise RuntimeError(f"Cannot enter {self!r} twice") _list = super().__enter__() # record=True means it's None. assert _list is not None self._list = _list warnings.simplefilter("always") return self def __exit__( self, exc_type: Optional[Type[BaseException]], exc_val: Optional[BaseException], exc_tb: Optional[TracebackType], ) -> None: if not self._entered: __tracebackhide__ = True raise RuntimeError(f"Cannot exit {self!r} without entering first") super().__exit__(exc_type, exc_val, exc_tb) # Built-in catch_warnings does not reset entered state so we do it # manually here for this context manager to become reusable. self._entered = False @final class WarningsChecker(WarningsRecorder): def __init__( self, expected_warning: Optional[ Union[Type[Warning], Tuple[Type[Warning], ...]] ] = Warning, match_expr: Optional[Union[str, Pattern[str]]] = None, *, _ispytest: bool = False, ) -> None: check_ispytest(_ispytest) super().__init__(_ispytest=True) msg = "exceptions must be derived from Warning, not %s" if expected_warning is None: warnings.warn(WARNS_NONE_ARG, stacklevel=4) expected_warning_tup = None elif isinstance(expected_warning, tuple): for exc in expected_warning: if not issubclass(exc, Warning): raise TypeError(msg % type(exc)) expected_warning_tup = expected_warning elif issubclass(expected_warning, Warning): expected_warning_tup = (expected_warning,) else: raise TypeError(msg % type(expected_warning)) self.expected_warning = expected_warning_tup self.match_expr = match_expr def __exit__( self, exc_type: Optional[Type[BaseException]], exc_val: Optional[BaseException], exc_tb: Optional[TracebackType], ) -> None: super().__exit__(exc_type, exc_val, exc_tb) __tracebackhide__ = True def found_str(): return pformat([record.message for record in self], indent=2) # only check if we're not currently handling an exception if exc_type is None and exc_val is None and exc_tb is None: if self.expected_warning is not None: if not any(issubclass(r.category, self.expected_warning) for r in self): __tracebackhide__ = True fail( f"DID NOT WARN. No warnings of type {self.expected_warning} were emitted.\n" f"The list of emitted warnings is: {found_str()}." ) elif self.match_expr is not None: for r in self: if issubclass(r.category, self.expected_warning): if re.compile(self.match_expr).search(str(r.message)): break else: fail( f"""\ DID NOT WARN. No warnings of type {self.expected_warning} matching the regex were emitted. Regex: {self.match_expr} Emitted warnings: {found_str()}""" )
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