feat: add basic tests for core storage module (#313)

* feat: add basic tests for core storage module

- Add 6 unit tests for FS struct and basic functionality
- Test FS creation, Debug and Clone trait implementations
- Test RUSTFS_OWNER constant definition and values
- Test S3 error code creation and handling
- Test compression format detection for common file types
- Include comprehensive documentation about integration test needs

Note: Full S3 API testing requires complex setup with storage backend,
global configuration, and network infrastructure - better suited for
integration tests rather than unit tests.

* style: fix code formatting issues

* fix: resolve clippy warnings in storage tests

---------

Co-authored-by: Cursor Agent <cursoragent@cursor.com>

rustfs/src/storage/ecfs.rs

@@ -3165,3 +3165,93 @@ impl S3 for FS {
         Ok(S3Response::new(output))
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_fs_creation() {
+        let _fs = FS::new();
+
+        // Verify that FS struct can be created successfully
+        // Since it's currently empty, we just verify it doesn't panic
+        // The test passes if we reach this point without panicking
+    }
+
+    #[test]
+    fn test_fs_debug_implementation() {
+        let fs = FS::new();
+
+        // Test that Debug trait is properly implemented
+        let debug_str = format!("{fs:?}");
+        assert!(debug_str.contains("FS"));
+    }
+
+    #[test]
+    fn test_fs_clone_implementation() {
+        let fs = FS::new();
+
+        // Test that Clone trait is properly implemented
+        let cloned_fs = fs.clone();
+
+        // Both should be equivalent (since FS is currently empty)
+        assert_eq!(format!("{fs:?}"), format!("{cloned_fs:?}"));
+    }
+
+    #[test]
+    fn test_rustfs_owner_constant() {
+        // Test that RUSTFS_OWNER constant is properly defined
+        assert!(!RUSTFS_OWNER.display_name.as_ref().unwrap().is_empty());
+        assert!(!RUSTFS_OWNER.id.as_ref().unwrap().is_empty());
+        assert_eq!(RUSTFS_OWNER.display_name.as_ref().unwrap(), "rustfs");
+    }
+
+    // Note: Most S3 API methods require complex setup with global state, storage backend,
+    // and various dependencies that make unit testing challenging. For comprehensive testing
+    // of S3 operations, integration tests would be more appropriate.
+
+    #[test]
+    fn test_s3_error_scenarios() {
+        // Test that we can create expected S3 errors for common validation cases
+
+        // Test incomplete body error
+        let incomplete_body_error = s3_error!(IncompleteBody);
+        assert_eq!(incomplete_body_error.code(), &S3ErrorCode::IncompleteBody);
+
+        // Test invalid argument error
+        let invalid_arg_error = s3_error!(InvalidArgument, "test message");
+        assert_eq!(invalid_arg_error.code(), &S3ErrorCode::InvalidArgument);
+
+        // Test internal error
+        let internal_error = S3Error::with_message(S3ErrorCode::InternalError, "test".to_string());
+        assert_eq!(internal_error.code(), &S3ErrorCode::InternalError);
+    }
+
+    #[test]
+    fn test_compression_format_usage() {
+        // Test that compression format detection works for common file extensions
+        let zip_format = CompressionFormat::from_extension("zip");
+        assert_eq!(zip_format.extension(), "zip");
+
+        let tar_format = CompressionFormat::from_extension("tar");
+        assert_eq!(tar_format.extension(), "tar");
+
+        let gz_format = CompressionFormat::from_extension("gz");
+        assert_eq!(gz_format.extension(), "gz");
+    }
+
+    // Note: S3Request structure is complex and requires many fields.
+    // For real testing, we would need proper integration test setup.
+    // Removing this test as it requires too much S3 infrastructure setup.
+
+    // Note: Testing actual S3 operations like put_object, get_object, etc. requires:
+    // 1. Initialized storage backend (ECStore)
+    // 2. Global configuration setup
+    // 3. Valid credentials and authorization
+    // 4. Bucket and object metadata systems
+    // 5. Network and disk I/O capabilities
+    //
+    // These are better suited for integration tests rather than unit tests.
+    // The current tests focus on the testable parts without external dependencies.
+}