32.5. Test Coverage Examination
  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 requires the
  
   gcov
  
  and
  
   lcov
  
  programs.
 
A typical workflow would look 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
  
  .
    The
  
   make
  
  commands also work in subdirectories.
 
To reset the execution counts between test runs, run:
make coverage-clean