Spring Boot: @TestConfiguration Not Overriding Bean During Integration Test

As documented in the Detecting Test Configuration section of the Spring Boot reference manual, any beans configured in a top-level class annotated with @TestConfiguration will not be picked up via component scanning. So you have to explicitly register your @TestConfiguration class.

You can do that either via @Import(MyTestConfiguration.class) or @ContextConfiguration(classes = MyTestConfiguration.class) on your test class.

On the other hand, if your class annotated with @TestConfiguration were a static nested class within your test class, it would be registered automatically.

Make sure that the method name of your @Bean factory method does not match any existing bean name. I had issues with method names like config() or (in my case) prometheusConfig() which collided with existing bean names. Spring skips those factory methods silently and simply does not call them / does not instantiate the beans.

If you want to override a bean definition in your test, use the bean name explicitly as string parameter in your @Bean("beanName") annotation.