Invalid failing example description with hypothesis.stateful.multiple containing single value

[lycantropos]

On my machine with Python 3.9.5 and hypothesis==6.37.1 (latest at the moment of writing) test case

from hypothesis.stateful import (Bundle,
                                 RuleBasedStateMachine,
                                 multiple,
                                 rule)


class State(RuleBasedStateMachine):
    values = Bundle('values')

    @rule(target=values)
    def create_single_multiple(self):
        return multiple(42)

    @rule(value=values)
    def check_value(self, value):
        assert value != 42


TestCase = State.TestCase

gives

Falsifying example:
    state = State()
    v1 = state.create_single_multiple()
    state.check_value(value=v1)
    state.teardown()

which will succeed because v1 is MultipleResults(values=(42,)) but I think it should be 42, so somewhere in depths of generating failing example for RuleBasedStateMachine we need to handle special case with single-value MultipleResults so the output will be

Falsifying example:
    state = State()
    v1, = state.create_single_multiple()
    # ^ note this comma
    state.check_value(value=v1)
    state.teardown()

[lycantropos]

I found a place in code which responsible for this behavior

hypothesis/hypothesis-python/src/hypothesis/stateful.py

Line 343 in 887e227

output_assignment = ", ".join(self._last_names(n_output_vars)) + " = "

I've managed to fix this locally by changing it to

            output_vars = self._last_names(n_output_vars)
            output_assignment = (output_vars[0] + ","
                                 if (isinstance(result, MultipleResults)
                                     and n_output_vars == 1)
                                 else ", ".join(output_vars)) + " = "