Can you give an example of a check that is too expensive to automate?

Checks that require complex configuration of external systems, large volumes of data, or long execution times are often too costly for automation. For example, performance tests with real user traffic or integration tests with many external services that are difficult to reliably emulate.

Example: automating the verification of the correctness of a payment system with real banks and processing centers — requires expensive infrastructure and can be unstable, so such tests are often performed manually or in a limited automated mode.