Prohibit circular references by default

Closes gh-27652

spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/context/runner/AbstractApplicationContextRunnerTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -23,7 +23,10 @@ import java.util.concurrent.atomic.AtomicBoolean;
 import com.google.gson.Gson;
 import org.junit.jupiter.api.Test;
 
+import org.springframework.beans.factory.BeanCurrentlyInCreationException;
 import org.springframework.beans.factory.BeanDefinitionStoreException;
+import org.springframework.beans.factory.ObjectProvider;
+import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.context.annotation.UserConfigurations;
 import org.springframework.boot.test.context.FilteredClassLoader;
 import org.springframework.boot.test.context.assertj.ApplicationContextAssertProvider;
@@ -181,6 +184,22 @@ abstract class AbstractApplicationContextRunnerTests<T extends AbstractApplicati
 		});
 	}
 
+	@Test
+	void runDisablesCircularReferencesByDefault() {
+		get().withUserConfiguration(ExampleConsumerConfiguration.class, ExampleProducerConfiguration.class)
+				.run((context) -> {
+					assertThat(context).hasFailed();
+					assertThat(context).getFailure().hasRootCauseInstanceOf(BeanCurrentlyInCreationException.class);
+				});
+	}
+
+	@Test
+	void circularReferencesCanBeAllowed() {
+		get().withAllowCircularReferences(true)
+				.withUserConfiguration(ExampleConsumerConfiguration.class, ExampleProducerConfiguration.class)
+				.run((context) -> assertThat(context).hasNotFailed());
+	}
+
 	@Test
 	void runWithUserBeanShouldBeRegisteredInOrder() {
 		get().withAllowBeanDefinitionOverriding(true).withBean(String.class, () -> "one")
@@ -250,4 +269,41 @@ abstract class AbstractApplicationContextRunnerTests<T extends AbstractApplicati
 
 	}
 
+	static class Example {
+
+	}
+
+	@FunctionalInterface
+	interface ExampleConfigurer {
+
+		void configure(Example example);
+
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	static class ExampleProducerConfiguration {
+
+		@Bean
+		Example example(ObjectProvider<ExampleConfigurer> configurers) {
+			Example example = new Example();
+			configurers.orderedStream().forEach((configurer) -> configurer.configure(example));
+			return example;
+		}
+
+	}
+
+	@Configuration(proxyBeanMethods = false)
+	static class ExampleConsumerConfiguration {
+
+		@Autowired
+		Example example;
+
+		@Bean
+		ExampleConfigurer configurer() {
+			return (example) -> {
+			};
+		}
+
+	}
+
 }