[apex][test] Rename apexutil tests to make the tests goal clear

Test: libapexutil_rust.test
Change-Id: Id5aa2b38d3939e11edf399003e74e95dabfc4cbe
diff --git a/libs/apexutil/src/lib.rs b/libs/apexutil/src/lib.rs
index 1183aea..999f16d 100644
--- a/libs/apexutil/src/lib.rs
+++ b/libs/apexutil/src/lib.rs
@@ -145,8 +145,9 @@
     use super::*;
 
     #[test]
-    fn test_open_apex() {
+    fn apex_verification_returns_valid_result() {
         let res = verify("tests/data/test.apex").unwrap();
+        // The expected hex is generated when we ran the method the first time.
         assert_eq!(
             to_hex_string(&res.root_digest),
             "fe11ab17da0a3a738b54bdc3a13f6139cbdf91ec32f001f8d4bbbf8938e04e39"
@@ -154,7 +155,7 @@
     }
 
     #[test]
-    fn test_payload_vbmeta_image_hash() {
+    fn payload_vbmeta_has_valid_image_hash() {
         let result = get_payload_vbmeta_image_hash("tests/data/test.apex").unwrap();
         assert_eq!(
             to_hex_string(&result),