Spring Forbid loading of a test's ApplicationContext in AOT mode if AOT processing failed

Overview

If AOT processing of a test's ApplicationContext failed, we should immediately fail an attempt to load the corresponding context when running in AOT mode.

For example, if a test class uses Spring Boot's @MockBean, AOT processing of that test's context will fail with a WARN log message, and there will no mapping from that test class to an AOT-generated ApplicationContextInitializer (ACI). Consequently, when the test suite is run in AOT mode that particular test class will fail with a confusing stack trace due to the fact that Spring Boot's SpringApplication attempts to locate a "main" ACI instead of the missing "test" ACI.

The TestContext framework should therefore never attempt to load an ApplicationContext in "JVM mode" while running in "AOT mode".

Deliverables

• [x] Rework the logic in DefaultCacheAwareContextLoaderDelegate.loadContext(...) to fail fast if an AOT-generated ACI cannot be found while running in AOT mode.