Tenant isolation that holds, and the test that proves it

The deliverable is the test, not the policy. The value is an assertion that goes red when isolation breaks, because every way it breaks here is silent: no error, no warning, no log line, and a catalog view that still reports the policy enabled.

Measured 2026-08-28 against a live engine reporting EngineEdition 5 and Edition SQL Azure. Open the measured runs when you need the statement behind a count or a message number below, or before changing one.

1. A filter predicate is not the boundary

Microsoft Learn states it plainly: the application can INSERT rows, even if they will be filtered during any other operation. Measured as a low-privilege user holding tenant id 1, filter predicate only: