Spring boot Test fails saying, Unable to start ServletWebServerApplicationContext due to missing ServletWebServerFactory bean

This message says: You need to configure at least 1 ServletWebServerFactory bean in the ApplicationContext, so if you already have spring-boot-starter-tomcat you need to either autoconfigure that bean or to do it manually.

So, in the test there are only 2 configuration classes to load the applicationContext, these are = { WebsocketSourceConfiguration.class, WebSocketSourceIntegrationTests.class }, then at least in one of these classes there should be a @Bean method returning an instance of the desired ServletWebServerFactory.

* SOLUTION *

Make sure to load all the beans within your configuration class

WebsocketSourceConfiguration {
  @Bean 
  ServletWebServerFactory servletWebServerFactory(){
  return new TomcatServletWebServerFactory();
  }
}

OR also enable the AutoConfiguration to do a classpath scanning and auto-configuration of those beans.

@EnableAutoConfiguration
WebsocketSourceConfiguration

Can be done also at the Integration Test class.

@EnableAutoConfiguration
WebSocketSourceIntegrationTests

For more information check the SpringBootTest annotation documentation https://docs.spring.io/spring-boot/docs/current/api/org/springframework/boot/test/context/SpringBootTest.html