Confused about data snooping before setting aside test set

I am really confused about what types of data exploration and inspection you are allowed to do on the whole dataset BEFORE setting aside the test set. In the end-to-end machine learning project demonstrated in Hands-On Machine Learning by Geron Aurelien, the author checks the following before setting aside a test set: 1) quantities of data points and null values, 2) value counts of each value in categorical columns, 3) statistical summary of numerical columns, including counts, mean, std, min, …

author checks data data exploration datascience dataset exploration machine machine learning project set test types