[PATCH 6/6] t/README: A new section about test coverage

@@ -267,6 +267,9 @@ Do:
 	git merge hla &&
 	git push gh &&
 	test ...
+    
+ - Check the test coverage for your tests. See the "Test coverage"
+   below.
 
 Don't:
 

@@ -508,3 +511,40 @@ the purpose of t0000-basic.sh, which is to isolate that level of
 validation in one place.  Your test also ends up needing
 updating when such a change to the internal happens, so do _not_
 do it and leave the low level of validation to t0000-basic.sh.
+
+Test coverage
+-------------
+
+You can use the coverage tests to find out if your tests are really
+testing your code code. To do that, run the coverage target at the
+top-level (not in the t/ directory):
+
+    make coverage
+    
+That'll compile Git with GCC's coverage arguments, and generate a test
+report with gcov after the tests finish. Running the coverage tests
+can take a while, since running the tests in parallel is incompatible
+with GCC's coverage mode.
+
+After the tests have run you can generate a list of untested
+functions:
+
+    make coverage-report-untested-functions
+
+You can also generate a detailed per-file HTML report using the
+Devel::Cover module. To install it do:
+
+   # On Debian:
+   sudo aptitude install libdevel-cover-perl
+
+   # From the CPAN with cpanminus
+   curl -L http://cpanmin.us | perl - --sudo --self-upgrade
+   cpanm --sudo Devel::Cover
+   
+Then, at the top-level:
+
+    make coverage-report-cover-db-html
+
+That'll generate a detailed cover report in the "cover_db_html"
+directory, which you can then copy to a webserver, or inspect locally
+in a browser.