UTs: update README

unittests/README.md

@@ -4,18 +4,28 @@
 
 Unit tests can be activate with ```configure --unittests```.
 
+Unit tests are executed each time a build occurs with ```make```. Execution of the tests happens as soon as possible and it will stop on errors. 
+
+## Notes
+
 Some unit tests require extra visibility of symbols. That's why a second build is required. This is done automatically.
 
-At the moment unit tests are executed each time a build occurs. Execution happens as soon as possible and it will stop the build on errors. Note: this processing could happen along with other reformatting and checks in a ```precommit``` command.
+Alternately you can run the tests with ```make unit_tests``` or look into ```unittests/launch.sh``` to set environment variable. Available options are ```--list``` (or ```-l```) and ```--only``` with a test number.
 
-# Writing unit tests
+The unit tests pre-processing could happen along with other reformatting and checks in a ```precommit``` command as part of developer's best practices.
+
+These tests are intented to complement existing tests from the testsuite.
+
+```gpac.c```also contains some unit tests of its own. They are unrelated to the runtime discussed in this document.
+
+## Writing a unit test
 
 Include the unit test framework:
 ```
 #include "tests.h"
 ```
 
-## Static function testing
+### Static function testing
 
 If the function is static, replace ```static``` with ```GF_STATIC```. If the function is not static and not exported while you need it, add ```GF_NOT_EXPORTED```. Then add a definition in your unit test file:
 ```
@@ -31,7 +41,7 @@ unittest(xml_translate_xml_string)
 }
 ```
 
-## Testing a full filter
+### Testing a full filter
 
 You can include the filter source code file in your test file. This has the advantage of allowing to reuse private contexts in the unit tests:
 ```