test(integration): develop tests for pipeline stages and workflow

[uwcdc]

Create integration tests to validate the functionality of each stage in the pipeline and ensure seamless operation of the end-to-end workflow.

Tasks:

• Write tests for individual pipeline stages (e.g., data download, preprocessing, R integration, S3 upload).

• Develop end-to-end tests that simulate the entire pipeline workflow.

• Automate test execution in the CI/CD pipeline.