Test CACHEDIR.TAG is created in an existing registry

Author: sourcefrog

tests/testsuite/registry.rs

@@ -1237,6 +1237,12 @@ fn updating_a_dep(cargo: fn(&Project, &str) -> Execs) {
         .run();
     assert!(paths::home().join(".cargo/registry/CACHEDIR.TAG").is_file());
 
+    // Now delete the CACHEDIR.TAG file: this is the situation we'll be in after
+    // upgrading from a version of Cargo that doesn't mark this directory, to one that
+    // does. It should be recreated.
+    fs::remove_file(paths::home().join(".cargo/registry/CACHEDIR.TAG"))
+        .expect("remove CACHEDIR.TAG");
+
     p.change_file(
         "a/Cargo.toml",
         r#"
@@ -1265,6 +1271,11 @@ fn updating_a_dep(cargo: fn(&Project, &str) -> Execs) {
 ",
         )
         .run();
+
+    assert!(
+        paths::home().join(".cargo/registry/CACHEDIR.TAG").is_file(),
+        "CACHEDIR.TAG recreated in existing registry"
+    );
 }
 
 #[cargo_test]