Add TEST_ASSUME macro to allow skipping tests at runtime

This commit adds a macro TEST_ASSUME to the test infrastructure
which allows to skip tests based on unmet conditions determined
at runtime.
diff --git a/tests/suites/main_test.function b/tests/suites/main_test.function
index 1574556..5d15f2b 100644
--- a/tests/suites/main_test.function
+++ b/tests/suites/main_test.function
@@ -159,7 +159,7 @@
     else
     {
         /* Unexpected parameter validation error */
-        test_info.failed = 1;
+        test_info.result = TEST_RESULT_FAILED;
     }
 
     memset( param_fail_jmp, 0, sizeof(jmp_buf) );