Worked on the Shopify/rails repository to improve HTTP header consistency by developing a regression test that verifies custom default headers configured through initializers are reliably applied to all HTTP responses. Addressed a timing race in the Rails initialization process, where ActionDispatch::Response could load before initializers completed, potentially leading to inconsistent header values. Utilized Ruby, Ruby on Rails, and integration testing to ensure that configuration changes in config.action_dispatch.default_headers are reflected in final responses. This work enhanced test coverage, reduced production risk related to header handling, and improved debugging visibility, contributing to more predictable and maintainable application behavior in production environments.