Restructure BeanOverrideBeanFactoryPostProcessor and improve documentation

spring-test/src/test/java/org/springframework/test/context/bean/override/mockito/MockitoSpyBeanTests.java

@@ -40,9 +40,9 @@ class MockitoSpyBeanTests {
 		assertThatIllegalStateException()
 				.isThrownBy(context::refresh)
 				.withMessage("""
-						Unable to override bean 'beanToSpy' by wrapping: \
-						there is no existing bean instance with that name of type %s""".formatted(
-						String.class.getName()));
+						Unable to override bean by wrapping: \
+						there is no existing bean definition with name [beanToSpy] and type [%s].""",
+						String.class.getName());
 	}
 
 	@Test