Is there a number limit for explanatory variables in this code? For example, can we use 7 explanatory variables?
If you are referring to the test published by Westerlund and Edgerton (2005), there is no limit to the number of explanatory variables that can be used. However, the moments used to compute the test statistic must be adjusted to account for the number of explanatory variables be included.
The original paper provides simulated moments for up to six explanatory variables. It can be found here.
If you are using more than 6 explanatory variables, you will need to bootstrap the moments, as explained in the paper.