The PostgreSQL source code can be compiled with coverage testing
    instrumentation, so that it becomes possible to examine which
    parts of the code are covered by the regression tests or any other
    test suite that is run with the code.  This is currently supported
    when compiling with GCC, and it requires the gcov
    and lcov programs.
   
A typical workflow looks like this:
./configure --enable-coverage ... OTHER OPTIONS ... make make check # or other test suite make coverage-html
    Then point your HTML browser
    to coverage/index.html.
   
    If you don't have lcov or prefer text output over an
    HTML report, you can run
make coverage
    instead of make coverage-html, which will
    produce .gcov output files for each source file
    relevant to the test.  (make coverage and make
    coverage-html will overwrite each other's files, so mixing them
    might be confusing.)
   
You can run several different tests before making the coverage report; the execution counts will accumulate. If you want to reset the execution counts between test runs, run:
make coverage-clean
    You can run the make coverage-html or make
    coverage command in a subdirectory if you want a coverage
    report for only a portion of the code tree.
   
    Use make distclean to clean up when done.