Modern C++ Programming with Test-Driven Development

8.6 Safe Refactoring to Support Testing

So that we can begin to add support for multiple channels, let’s figure out where it might be useful to verify functionality in the ​open​ function.

Near its end appears a number of calculations—total seconds, how many samples to write, where to start, and so on. After all these calculations is a ​for​ loop that appears to write samples to an output file. (This chunk of code appears highlighted in the earlier listing of ​open​ .) We’ll need to change a calculation or two plus fix the loop in order to support multiple channels.

The most interesting piece of code is the loop. Let’s write tests around that...but how? We’d need to set up lots of information to get that far in the ​open​ function.

Instead, let’s ...