test_slider_zoom_in_with_touch fails because pinch gesture doesn't work

Currently this test is failing with this error:

Traceback (most recent call last):
  File "/home/phablet/autopilot/camera_app/tests/test_zoom.py", line 54, in test_slider_zoom_in
    zoom_control.value, Eventually(Equals(zoom_control.maximumValue)))
  File "/usr/lib/python3/dist-packages/testtools/testcase.py", line 406, in assertThat
    raise mismatch_error
testtools.matchers._impl.MismatchError: After 10.0 seconds test on ZoomControl.value failed: 59.0 != dbus.Double(1.0, variant_level=1)

Following the tests, it seems that the pinch gesture that's being attempted in the test is not being registered. Instead it seems to be registering a press on the screen (because the focus graphic appears). Pinching manually works, so there is nothing wrong there.