Seems like BCG is really active globally, since many people are asking about various steps of the process with them.
The online quant test are indeed very similar among them and hence, better to prep.
I would strongly recomment you practice it with the Integrated Reasoning part of the GMAT exam.
There are free exams in the internet that you can use for practice (the one of LBS MBA page, Verits prep, as well as some free trials for courses such as the one of The Economist (https://gmat.economist.com/)
The old McKinsey PST, Bain SOVA test, etc. are all quite similar so leverage resources across all of them.
Hope it helps!
The online tests across companies are very similar
Format? Somewhat. Content and what's required from you ability-wise? Not at all.
The best way is to really find online tests / questions and practice. Regardless as to whether is a new or old test, the principles are mostly the same:
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.
The (old) McKinsey PST, BCG Online Test, Bain SOVA test, etc. are all quite similar so leverage resources across all of them.
For most of these tests, the GMAT, especially the integrated reasoning provides a good proxy. Check out GMATClub and other free resources at Veritas, Manhattan Prep and The Economist to prepare for this type of questions and way of thinking.
You will be given 45 minutes for 23 questions.
Regarding the question types
You need to be good at reading charts, analytical thinking and mental math.
I have created one for practice, you can try it as well
Do you have any further questions?