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TDD helps close to 0 % with fragility and only exists to help development

It doesn't. All those unit tests don't guarantee you have a working system, especially when everything is mocked out (which is often the case.)

End-to-end and integration tests are much more helpful. But even then, they won't look at operational concerns like backup and recovery.

TDD not really. Having tests help, writing them first is irrelevant

How would you apply TDD to a backup system? By writing backup and restore tests? What if one test fails unreproducibly?

Well, you should test your backups. But TDD is entirely unrelated to the problem aside from including "test" in the name