### Question:
BivariateDataStatisticsCalculator { public double xMean() { return xData.mean().scalar(); } BivariateDataStatisticsCalculator(DoubleTensor xData, DoubleTensor yData); long size(); double xMean(); double yMean(); double estimatedGradient(); double estimatedIntercept(); double meanSquaredError(); double standardErrorForGradient(); double standardErrorForIntercept();  }### Answer:
@Test public void youCanGetTheMeanOfX() { assertThat(stats.xMean(), equalTo(xStats.getMean())); }