Add linker.config.pb test

In apex, ./etc/linker.config.pb file should be readable by linkerconfig.

Bug: 218922042
Test: apex_sepolicy_tests_test
Change-Id: Id41710dc127b5f5bda2d5bbb65271bcc0c5179b1
diff --git a/tests/apex_sepolicy_tests_test.py b/tests/apex_sepolicy_tests_test.py
index 125290c..9b427a0 100644
--- a/tests/apex_sepolicy_tests_test.py
+++ b/tests/apex_sepolicy_tests_test.py
@@ -88,6 +88,11 @@
         self.assert_ok('./etc/init.x32rc u:object_r:vendor_file:s0')
         self.assert_ok('./etc/init.x32rc u:object_r:unknown:s0')
 
+    def test_linkerconfig(self):
+        self.assert_ok('./etc/linker.config.pb u:object_r:system_file:s0')
+        self.assert_ok('./etc/linker.config.pb u:object_r:linkerconfig_file:s0')
+        self.assert_error('./etc/linker.config.pb u:object_r:vendor_file:s0',
+                        r'Error: .*linkerconfig.* can\'t read')
 
 if __name__ == '__main__':
     unittest.main(verbosity=2)