def eventual_result(self, stream, checker):
name = stream.name + '<STR_LIT>'<EOL>cond = sttrt._EventualResult(checker, name)<EOL>self.topology.graph.add_dependency(checker)<EOL>return self.add_condition(stream, cond)<EOL>
Test a stream reaches a known result or state.

        Creates a test condition that the tuples on a stream
        eventually reach a known result or state. Each tuple
        on `stream` results in a call to ``checker(tuple_)``.

        The return from `checker` is handled as:
            * ``None`` - The condition requires more tuples to become valid.
            * `true value` - The condition has become valid.
            * `false value` - The condition has failed. Once a condition has failed it can never become valid.

        Thus `checker` is typically stateful and allows ensuring that
        condition becomes valid from a set of input tuples. For example
        in a financial application the application under test may need
        to achieve a final known balance, but due to timings of windows the
        number of tuples required to set the final balance may be variable.

        Once the condition becomes valid any false value,
        except ``None``, returned by processing of subsequent
        tuples will cause the condition to fail.

        Returning ``None`` effectively never changes the state of the condition.

        Args:
            stream(Stream): Stream to be tested.
            checker(callable): Callable that returns evaluates the state of the stream with result to the result.

        .. versionadded:: 1.11