def test_exponential_model_mean_var():
model = ExponentialModel(shape=0.001, rate=0.001)
assert np.isnan(model.ppmean())
assert np.isnan(model.ppvar())
def test_exponential_model_stats():
model = ExponentialModel(shape=25, rate=1000)
assert model.ppmean() == approx(41.66666666)
assert model.ppvar() == approx(1887.077294)