Class WarningsChecker

src/_pytest/recwarn.py:231–296

@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

        # 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(
                        "DID NOT WARN. No warnings of type {} were emitted. "
                        "The list of emitted warnings is: {}.".format(
                            self.expected_warning, [each.message for each in self]
                        )
                    )
                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(