I applied online through the BCG careers page. After about a week, I received an email inviting me to complete a proctored CodeSignal Data Science Framework assessment. The assessment was 90 minutes long and contained 5 questions covering data cleaning, data preprocessing, training a ML classifier, aggregating data from multiple files using joins and groupbys, and a probability calculation. The time pressure was significant. I did not advance past this stage.

The interviewer was very friendly, he explained everything I think he did not leave anything out in terms of salary and benefits, he also explained what would be needed for the technical assessment. In my case, Python (Numpy, Pandas, Scikit-learn).