'make sure all the empty position stats return a numeric 0
Originally this bug was due to np.dot([], []) returning
np.bool_(False)'

def test_empty_positions(self):

    sim_params = factory.create_simulation_parameters(num_days=4)
    pt = perf.PositionTracker(sim_params.data_frequency)
    pos_stats = pt.stats()
    stats = ['net_value', 'net_exposure', 'gross_value', 'gross_exposure', 'short_value', 'short_exposure', 'shorts_count', 'long_value', 'long_exposure', 'longs_count']
    for name in stats:
        val = getattr(pos_stats, name)
        self.assertEquals(val, 0)
        self.assertNotIsInstance(val, (bool, np.bool_))
