Revise bean override tests with a focus on AOT support

As a follow up to the previous commit (31f8e12adb), this commit
polishes bean override tests and revises them with a focus on AOT
testing support and simplified maintenance.

- Introduce EngineTestKitUtils to simplify working with JUnit's
  EngineTestKit.

- Use idiomatic EngineTestKit APIs to simplify assertions on
  EngineTestKit results.

- Introduce BeanOverrideTestSuite to simplify running all bean override
  tests within the IDE.

- Separate failure and success scenario tests, so that failure tests do
  not launch the JUnit Platform to run tests using the Spring
  TestContext Framework (TCF) within a test class that itself uses the
  TCF.

- Make AbstractTestBeanIntegrationTestCase actually abstract.

- Rename test case classes to give them meaningful names and simplify
  understanding of what's being tested.

- Ensure tests for @⁠MockitoSpyBean functionality use @⁠MockitoSpyBean
  instead of @⁠MockitoBean.

- Declare @⁠Configuration classes local to @⁠SpringJUnitConfig test
  classes whenever possible.

See gh-29122
See gh-32925

spring-test/src/main/java/org/springframework/test/context/bean/override/BeanOverrideBeanFactoryPostProcessor.java

@@ -133,7 +133,7 @@ class BeanOverrideBeanFactoryPostProcessor implements BeanFactoryPostProcessor,
 			Set<String> candidates = getExistingBeanNamesByType(beanFactory, overrideMetadata, true);
 			if (candidates.size() != 1) {
 				Field f = overrideMetadata.getField();
-				throw new IllegalStateException("Unable to select a bean definition to override, " +
+				throw new IllegalStateException("Unable to select a bean definition to override: " +
 						candidates.size() + " bean definitions found of type " + overrideMetadata.getBeanType() +
 						" (as required by annotated field '" + f.getDeclaringClass().getSimpleName() +
 						"." + f.getName() + "')");
@@ -147,7 +147,7 @@ class BeanOverrideBeanFactoryPostProcessor implements BeanFactoryPostProcessor,
 				existingBeanDefinition = beanFactory.getBeanDefinition(beanName);
 			}
 			else if (enforceExistingDefinition) {
-				throw new IllegalStateException("Unable to override bean '" + beanName + "'; there is no" +
+				throw new IllegalStateException("Unable to override bean '" + beanName + "': there is no" +
 						" bean definition to replace with that name of type " + overrideMetadata.getBeanType());
 			}
 		}
@@ -183,7 +183,7 @@ class BeanOverrideBeanFactoryPostProcessor implements BeanFactoryPostProcessor,
 			Set<String> candidateNames = getExistingBeanNamesByType(beanFactory, metadata, true);
 			if (candidateNames.size() != 1) {
 				Field f = metadata.getField();
-				throw new IllegalStateException("Unable to select a bean to override by wrapping, " +
+				throw new IllegalStateException("Unable to select a bean to override by wrapping: " +
 						candidateNames.size() + " bean instances found of type " + metadata.getBeanType() +
 						" (as required by annotated field '" + f.getDeclaringClass().getSimpleName() +
 						"." + f.getName() + "')");
@@ -193,7 +193,7 @@ class BeanOverrideBeanFactoryPostProcessor implements BeanFactoryPostProcessor,
 		else {
 			Set<String> candidates = getExistingBeanNamesByType(beanFactory, metadata, false);
 			if (!candidates.contains(beanName)) {
-				throw new IllegalStateException("Unable to override bean '" + beanName + "' by wrapping; there is no" +
+				throw new IllegalStateException("Unable to override bean '" + beanName + "' by wrapping: there is no" +
 						" existing bean instance with that name of type " + metadata.getBeanType());
 			}
 		}