All our education/work documents being in French (native) or English, we just wrote a letter detailing our studies in France and UK then our work in the UK for the last 4 years. Do you have official documents, degrees, work contracts etc in French or English? This may not be anough, I don't know.
French as 1st is OK for us (born and lived in France for over 20 years, uni degrees etc which we sent), as for English we did consider a test, but looking at the points for the second language it was something like: (not 100% sure)
High proficiency: 2 2 2 2
Basic profiency: 2 2 2 2
Good: 1 1 1 1
I do remember that there was no point difference for the top and middle "scores", so we thought our evidence of studying and working in the UK for 5 years would be enough to get at the very least 1 1 1 1- we still wrote that letter to explain that. Of course this is for the second language. For a first language as there are so many points involved and it's a key requirement I would say go for safer, do the tests unless you have a strong case you can explain to them with supporting evidence in English.