'Tests Negative Binomial family with canonical link
g(p) = log(p/(p + 1/alpha))'

@classmethod
def setup_class(cls):

    super(TestWtdGlmNegativeBinomial, cls).setup_class()
    alpha = 1.0
    family_link = sm.families.NegativeBinomial(link=sm.families.links.nbinom(alpha=alpha), alpha=alpha)
    cls.res1 = GLM(cls.endog, cls.exog, freq_weights=cls.weight, family=family_link).fit()
    cls.res2 = GLM(cls.endog_big, cls.exog_big, family=family_link).fit()
