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Testing with `psygnal`#

If you would like to test to ensure that signals are emitted (or not emitted) as expected, you can use the convenience functions in the psygnal.testing module.

Examples#

The easiest approach is to use one of the assert_* context managers. These temporarily listen to a signal and check if it is emitted (or not emitted) when the context is exited. The API closely mirrors the unittest.mock API, with the word "called" replaced with "emitted".

from psygnal import Signal
import psygnal.testing as pt

class MyObject:
    changed = Signal()
    value_changed = Signal(int)

def test_my_object():
    obj = MyObject()

    with pt.assert_emitted(obj.changed):
        obj.changed.emit()

    with pt.assert_not_emitted(obj.value_changed):
        obj.changed.emit()

    with pt.assert_emitted_once(obj.value_changed):
        obj.value_changed.emit(42)

    with pt.assert_emitted_once_with(obj.value_changed, 42):
        obj.value_changed.emit(42)

    with pt.assert_ever_emitted_with(obj.value_changed, 42):
        obj.value_changed.emit(41)
        obj.value_changed.emit(42)
        obj.value_changed.emit(43)

All of the context managers yield an instance of SignalTester, which can be used to check the number of emissions and the arguments. It may also be used directly:

from psygnal import Signal
import psygnal.testing as pt

class MyObject:
    value_changed = Signal(int)

def test_my_object():
    obj = MyObject()
    tester = pt.SignalTester(obj.value_changed)

    with tester:
        obj.value_changed.emit(42)
        obj.value_changed.emit(43)

    assert tester.emit_count == 2
    assert tester.emit_args_list == [(42,), (43,)]
    assert tester.emit_args == (43,)
    tester.assert_ever_emitted_with(42)
    tester.assert_emitted_with(43)

See API documentation for SignalTester for more details.