Yes, you should expect the BCG Online Test. The best way to be clear on this is to ask HR what you should expect for the interview.
That being said, you are likely to have to take a 1-hour version of the BCG online test, which includes you taking a multiple-choice test as well as completing a video recording.
Think of it as a merge of a case and the GMAT/GRE.
You need to be clear on some key case-related and account formulas (margin, growth, breakeven, etc) as well as be good at critically understanding the question (including nuance to questions) and parsing through complicated text with a fair amount of distraction.
You'll also need to be good at chart/graph reading.
There an excellent guide:
I also have a practice test - shoot me a message and I can send it your way!