Hypothesis testing of single normal total variance

It is known that the overall <i>X</i> obeys a normal distribution with a mean of μ, a standard deviation of σ, and a variance of σ², ie <i>X</i>~<i> N</i>(μ,σ²), This page deals with the case where the mean value is unknown to the other party's difference hypothesis test, and the test statistic is

<img align="middle" alt="" src="http://drr.ikcest.org/static/upload/6e/6eca1f60-ecbf-11e9-80df-00163e0618d6_m.jpg" style="width: 120px;" >。