aconfig: add test utilities

Create a test utility function to create a Cache from the files in
testdata/*. A follow-up CL will update the unit tests to use this
instead of creating their own caches.

Bug: 283910447
Test: atest aconfig.test
Change-Id: Ice5064eadb0babde5eb38d292330d213ab136d96
diff --git a/tools/aconfig/src/codegen_rust.rs b/tools/aconfig/src/codegen_rust.rs
index b3a6f53..6d60323 100644
--- a/tools/aconfig/src/codegen_rust.rs
+++ b/tools/aconfig/src/codegen_rust.rs
@@ -79,28 +79,10 @@
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::commands::{create_cache, Input, Source};
 
     #[test]
     fn test_generate_rust_code() {
-        let cache = create_cache(
-            "test",
-            vec![Input {
-                source: Source::File("testdata/test.aconfig".to_string()),
-                reader: Box::new(include_bytes!("../testdata/test.aconfig").as_slice()),
-            }],
-            vec![
-                Input {
-                    source: Source::File("testdata/first.values".to_string()),
-                    reader: Box::new(include_bytes!("../testdata/first.values").as_slice()),
-                },
-                Input {
-                    source: Source::File("testdata/test.aconfig".to_string()),
-                    reader: Box::new(include_bytes!("../testdata/second.values").as_slice()),
-                },
-            ],
-        )
-        .unwrap();
+        let cache = crate::test::create_cache();
         let generated = generate_rust_code(&cache).unwrap();
         assert_eq!("src/lib.rs", format!("{}", generated.path.display()));
         let expected = r#"