def METHOD_NAME(self, volatility):
    explore = PerturbExplore(factor=1.0, volatility=volatility)
    rng = RNGStub()
    rng.random = lambda: 1.0
    rng.normal = lambda mean, variance: variance
    assert explore.perturb_real(rng, 3.0, (1.0, 2.0)) == 2.0 - volatility