Three issues fixed in processing_issues_test.go:
- Empty UUID: handler returns 400 (uuid.Parse rejects empty string), not 404.
Fix expectedStatus in both List and Stats validation tests.
- Path traversal: raw '../../' in URL creates extra path segments that don't
match the route. Use url.PathEscape so the string is treated as a single
path parameter, letting the handler reject it with 400.
- SQL injection: raw special characters (semicolons, quotes) caused
httptest.NewRequest to panic. url.PathEscape prevents the panic and the
handler rejects the decoded value via uuid.Parse.
- Remove unsupported 'audiobooks' library type from
TestProcessingIssuesDifferentLibraryTypes (only ebooks/comics/manga exist
in the database schema).