How would you test an OmniStudio solution, given that the components are largely declarative?

The absence of a unit test framework for declarative components does not remove the obligation to test; it changes where the effort goes.

1. Component-level preview: Data Mappers and Integration Procedures have preview and debug capability that lets you run them with representative input and inspect the output. Keep a documented set of input payloads and expected outputs for each and re-run them after changes.
2. Apex test coverage for any remote or invocable classes the procedures call — this part is conventional and should be held to normal standards.
3. Jest tests for custom LWC embedded in OmniScripts or FlexCards.
4. Persona-based end-to-end testing. Because Data Mappers run in the caller's context, testing as an administrator proves very little. Run the flow as each real persona, in a sandbox with representative data volumes.
5. Regression on shared components. An Integration Procedure used by four OmniScripts needs all four exercised when it changes; keep a dependency map so this is not guesswork.
6. Negative paths: external service down, user lacking a field, empty result sets, and the back-button path where a user changes an earlier answer after data has already been fetched.