So how does OpenCover's profiling impact your testing. The best way is to get some figures so that you can judge for yourself.
I decided to use OpenCover's own tests and use the timing value produced by Nunit itself; just like I'd expect any user who is trying to determine impact I suppose. I've also added the results from PartCover for comparison. Before I took any numbers I (warmed) the code by running the code several times beforehand.
Nunit32
Nunit32 (OpenCover)
Nunit32 (PartCover)
Nunit64
Nunit64 (OpenCover)
2.643
2.691
2.639
4.544
3.807
2.629
2.69
2.611
4.426
3.753
2.642
2.638
2.612
4.46
4.036
Average
2.638
2.673
2.621
4.477
3.865
I don't know how to interpret these results as they don't make much sense, OpenCover seemed to add on average 1.3% to the total time (which I'd expect), whereas PartCover appears to make the code go faster by 0.64%. I can't explain why the results for 64 bit seem to show that OpenCover improves performance by 13.6%.
I tried to come up with a number of reasons for the above but the results I keep getting are reasonably consistent, so I decided to post them anyway and perhaps someone else will be able to tell me what is happening.