Error out if script is missing when collecting test cases

Signed-off-by: Pengyu Lv <pengyu.lv@arm.com>
diff --git a/tests/scripts/check_test_cases.py b/tests/scripts/check_test_cases.py
index 39bf73c..d67e678 100755
--- a/tests/scripts/check_test_cases.py
+++ b/tests/scripts/check_test_cases.py
@@ -149,8 +149,7 @@
 
             for sh_file in ['ssl-opt.sh', 'compat.sh']:
                 sh_file = os.path.join(directory, sh_file)
-                if os.path.exists(sh_file):
-                    self.collect_from_script(sh_file)
+                self.collect_from_script(sh_file)
 
 class TestDescriptions(TestDescriptionExplorer):
     """Collect the available test cases."""