How does covr work anyway?
Introduction | Instrumenting R Source Code | Modifying the call tree | Source References | Refining Source References | Replacing Source In Place | Object Orientation | S3 Classes | S4 Classes | Reference Classes | Compiled code | Gcov | Makevars | Subprocess | Output Formats | Codecov.io and Coveralls.io | Prior Art | Overview | R-coverage | Test Coverage | Covr | Conclusion