Update test

The purpose of this test is to validate that metadata stays valid between versions. However the Ruby version change between default version bumps was causing a cache invalidation. This test is made more robust by specifying an explicit Ruby version

Author: schneems

buildpacks/ruby/tests/integration_test.rs

@@ -10,6 +10,7 @@ use libcnb_test::{
 };
 use pretty_assertions::assert_eq;
 use regex::Regex;
+use std::io::Write;
 use std::os::unix::fs::PermissionsExt;
 use std::path::{Path, PathBuf};
 use std::thread;
@@ -24,14 +25,38 @@ fn test_migrating_metadata_or_layer_names() {
     // This test is a placeholder for when a change modifies metadata structures.
     // Remove the return and update the `buildpack-ruby` reference to the latest version.
     #![allow(unreachable_code)]
-    // Test v5.0.1 compatible with v5.0.0
+    // Test v7.0.0 compatible with v6.0.0
 
     let builder = "heroku/builder:24";
-    let app_dir = "tests/fixtures/default_ruby";
+    let temp = tempfile::tempdir().unwrap();
+    let app_dir = temp.path();
+
+    copy_dir_all(
+        PathBuf::from(env!("CARGO_MANIFEST_DIR"))
+            .join("tests")
+            .join("fixtures")
+            .join("default_ruby"),
+        app_dir,
+    )
+    .unwrap();
+
+    // Specify explicit versions so changes in default values don't cause this test to fail
+    writeln!(
+        fs_err::OpenOptions::new()
+            .write(true)
+            .append(true)
+            .open(app_dir.join("Gemfile.lock"))
+            .unwrap(),
+        indoc! {"
+                RUBY VERSION
+                   ruby 3.4.2
+            "}
+    )
+    .unwrap();
 
     TestRunner::default().build(
         BuildConfig::new(builder, app_dir).buildpacks([BuildpackReference::Other(
-            "docker://docker.io/heroku/buildpack-ruby:5.0.0".to_string(),
+            "docker://docker.io/heroku/buildpack-ruby:6.0.0".to_string(),
         )]),
         |context| {
             println!("{}", context.pack_stderr);