add signals_blocked util (#69)

tests/test_utils.py

@@ -0,0 +1,29 @@
+from unittest.mock import Mock
+
+from qtpy.QtCore import QObject, Signal
+
+from superqt.utils import signals_blocked
+
+
+def test_signal_blocker(qtbot):
+    """make sure context manager signal blocker works"""
+
+    class Emitter(QObject):
+        sig = Signal()
+
+    obj = Emitter()
+    receiver = Mock()
+    obj.sig.connect(receiver)
+
+    # make sure signal works
+    with qtbot.waitSignal(obj.sig):
+        obj.sig.emit()
+
+    receiver.assert_called_once()
+    receiver.reset_mock()
+
+    with signals_blocked(obj):
+        obj.sig.emit()
+        qtbot.wait(10)
+
+    receiver.assert_not_called()