Write and run unit tests for custom Omni Gateway policies built with the Policy Development Kit (PDK) — wire up `src/tests/`, build a first `UnitTestBuilder` test, mock HTTP/gRPC upstreams with closures or `TraceBackend`, factor reusable `TestConfig` helpers, assert on responses / headers / violations, run with `make test` or `cargo test`, troubleshoot init-sleep races, authority mismatches, and feature-gate skew. Use whenever the user mentions "PDK unit test", "pdk-unit", "UnitTestBuilder", "test my policy", "cargo test PDK", "mock backend PDK", "Omni Gateway policy unit testing", `with_http_upstream_from_authority`, `with_entrypoint`, `TraceBackend`, or asks "how do I test an Omni Gateway policy", "how do I mock an upstream in pdk-unit", "why is my policy timer not firing in tests". For full `pdk-unit` API reference see `pdk-templates/templates/unit_testing.md`. For scaffolding / build / publish see `develop-pdk-policy`.