Affects versions: 2.5.7+

I believe this is result of moving this line, see details below.

Our Spring Boot application has explicit dependency to spring-boot-starter-webflux and transitive dependency to spring-boot-starter-web, but in test/resources/application.properties we declared:

spring.main.web-application-type=reactive 

and we've got test:

@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT) // (1) class ReactiveOrServletApplicationTests { @Autowired(required = false) private org.springframework.boot.web.servlet.error.ErrorAttributes errorAttributesServlet; // (2) @Autowired(required = false) private org.springframework.boot.web.reactive.error.ErrorAttributes errorAttributesReactive; @Test void contextLoads() { assertThat(errorAttributesServlet).isNull(); assertThat(errorAttributesReactive).isNotNull(); } }

Please note:

• (1) is important to declare webEnvironment because if effectively creates AbstractBeanFactory.scopes empty. That's important because of Respect WebApplicationType.REACTIVE in tests with a mock web environment #29170

• (2) we try to inject some servlet component, we expect null

Running such tests will fail, because Spring will try to define conflicting beans:

• org.springframework.boot.web.servlet.error.DefaultErrorAttributes (from ErrorMvcAutoConfiguration)
• org.springframework.boot.web.reactive.error.DefaultErrorAttributes (from ErrorWebFluxAutoConfiguration)

Such tests correctly passes on 2.5.6.

Mentioned change effectively changes what will be assigned here:

Before change it was StandardEnvironment, after change it is ApplicationServletEnvironment. Difference changes evaluation (from false to true) in:

And this messes with type of web application:

 ErrorMvcAutoConfiguration matched: - @ConditionalOnClass found required classes 'javax.servlet.Servlet', 'org.springframework.web.servlet.DispatcherServlet' (OnClassCondition) - found ConfigurableWebEnvironment (OnWebApplicationCondition)