Clarify the descriptions of test-case-data-related modules

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/scripts/mbedtls_dev/test_case.py b/scripts/mbedtls_dev/test_case.py
index 6a46e42..d8f7b60 100644
--- a/scripts/mbedtls_dev/test_case.py
+++ b/scripts/mbedtls_dev/test_case.py
@@ -1,4 +1,4 @@
-"""Library for generating Mbed TLS test data.
+"""Library for constructing an Mbed TLS test case.
 """
 
 # Copyright The Mbed TLS Contributors