Add tests

tests/data/accesstransformer/hidden_prefix/accesstransformer.cfg

@@ -0,0 +1 @@
+public C1

tests/data/accesstransformer/hidden_prefix/expected/C1.java

@@ -0,0 +1,3 @@
+public class C1 {
+    C1() {}
+}

tests/data/accesstransformer/hidden_prefix/source/C1.java

@@ -0,0 +1,2 @@
+class C1 {
+}

tests/data/accesstransformer/hidden_prefix/source/other/C2f.java

@@ -0,0 +1,5 @@
+package other;
+
+final class C2f {
+
+}

tests/src/test/java/net/neoforged/jst/tests/EmbeddedTest.java

@@ -297,6 +297,11 @@ void testMethodsNoInheritance() throws Exception {
         void testMethodsInheritance() throws Exception {
             runATTest("methods_inheritance", "--access-transformer-inherit-method");
         }
+
+        @Test
+        void testHiddenPrefixes() throws Exception {
+            runATTest("hidden_prefix", "--hidden-prefix=other");
+        }
     }
 
     @Nested