lean2/doc/make/coverage.md

Instructions for Testing and Measuring Code Coverage

To measure code coverage, compile TESTCOV build using g++:

mkdir -p build/testcov
cd build/testcov
cmake -DCMAKE_BUILD_TYPE=Debug -DTESTCOV=ON -DCMAKE_CXX_COMPILER=g++-4.8 -G Ninja ../../src

and run:

ninja cov

It will build the project, run testcases, and compute code-coverage. In the end, you have build/testcov/coverage directory containing a code-coverage report in HTML format.

Note: make sure that the version of gcov matches with the one of g++. Also try to use the latest lcov if you have a problem with the existing one.