import mir.math.sum: Summation;
import mir.ndslice.slice: sliced;
import mir.test: shouldApprox;

auto x = [  0.0,   1.0,   1.5,  2.0,  3.5, 4.25,
            2.0,   7.5,   5.0,  1.0,  1.5,  0.0].sliced;
auto y = [-0.75,   6.0, -0.25, 8.25, 5.75,  3.5,
           9.25, -0.75,   2.5, 1.25,   -1, 2.25].sliced;

auto v = CovarianceAccumulator!(double, CovarianceAlgo.twoPass, Summation.naive)(x, y);

v.covariance(true).shouldApprox == -5.5 / 12;
v.covariance(false).shouldApprox == -5.5 / 11;