test(fs): add tests

src/fs/real.rs

@@ -57,11 +57,11 @@ impl super::FileSystemLike for RealFileSystem {
 
 impl RealFileSystem {
     fn validate(&self, path: &Path) -> super::Result<()> {
-        let path = self.clean_path(path)?;
-        if !path.starts_with(&self.base) {
+        let canon = self.clean_path(path)?;
+        if !canon.starts_with(&self.base) {
             return Err(super::Error::PathTraversal {
                 base: self.base.clone(),
-                path,
+                path: canon.to_path_buf(),
             });
         }
         Ok(())