kunit_tool: add tests for method build_reconfig()

added tests for build_reconfig() and build_config() - tested for
make_olddefconfig() adding and deleting lines from the .config
file.

Signed-off-by: Darya Verzhbinsky <daryaver@google.com>
Signed-off-by: Maria Del Carmen Ignacio <mariaignacio@google.com>
Change-Id: Id29559f67beb86fb4504d14016a1c4e9a00e9667
1 file changed