[shill] Add info about incremental edit/compile/test/debug

BUG=None
TESTS=None; it's a text file change.

Change-Id: I5397a883739f4740ea9e8e9857223435ea9c21e6
Reviewed-on: https://gerrit.chromium.org/gerrit/10738
Tested-by: Chris Masone <cmasone@chromium.org>
Commit-Ready: Chris Masone <cmasone@chromium.org>
Reviewed-by: mukesh agrawal <quiche@chromium.org>
diff --git a/TESTING b/TESTING
index e406aa0..5331229 100644
--- a/TESTING
+++ b/TESTING
@@ -22,6 +22,13 @@
   step since the build directory would have been retained in the course
   of the test failing.)
 
+- for an incremental workflow, you can setup like this:
+  (chroot)$ cros_workon --board x86-generic shill
+- incrementally build like this:
+  (chroot)$ CXXFLAGS=-g cros_workon_make --board x86-generic --reconf --test shill
+- and then debug tests like this:
+  (chroot)$ gdb_x86_local --board x86-generic /path/to/checkout/src/platform/shill/shill_unittest
+
 Running integration tests
 -------------------------
 - build a test image, suitable for a VM: