Fix primary beans with ApplicationContextAssert

Update `ApplicationContextAssert.getBean` so that multiple beans are
supported as long as one of them is primary. This aligns better with
the way that the standard `ApplicationContext.getBean` method works.

Closes gh-14874

spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/context/assertj/ApplicationContextAssert.java

@@ -32,8 +32,10 @@ import org.assertj.core.error.BasicErrorMessageFactory;
 
 import org.springframework.beans.factory.BeanFactoryUtils;
 import org.springframework.beans.factory.NoSuchBeanDefinitionException;
+import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
 import org.springframework.context.ApplicationContext;
+import org.springframework.context.ConfigurableApplicationContext;
 import org.springframework.util.Assert;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -273,17 +275,49 @@ public class ApplicationContextAssert<C extends ApplicationContext>
 					"to contain bean of type:%n <%s>", type));
 		}
 		String[] names = scope.getBeanNamesForType(getApplicationContext(), type);
-		if (names.length > 1) {
+		String name = (names.length > 0) ? getPrimary(names, scope) : null;
+		if (names.length > 1 && name == null) {
 			throwAssertionError(new BasicErrorMessageFactory(
 					"%nExpecting:%n <%s>%nsingle bean of type:%n <%s>%nbut found:%n <%s>",
 					getApplicationContext(), type, names));
 		}
-		T bean = (names.length != 0) ? getApplicationContext().getBean(names[0], type)
-				: null;
+		T bean = (name != null) ? getApplicationContext().getBean(name, type) : null;
 		return Assertions.assertThat(bean).as("Bean of type <%s> from <%s>", type,
 				getApplicationContext());
 	}
 
+	private String getPrimary(String[] names, Scope scope) {
+		if (names.length == 1) {
+			return names[0];
+		}
+		String primary = null;
+		for (String name : names) {
+			if (isPrimary(name, scope)) {
+				if (primary != null) {
+					return null;
+				}
+				primary = name;
+			}
+		}
+		return primary;
+	}
+
+	private boolean isPrimary(String name, Scope scope) {
+		ApplicationContext context = getApplicationContext();
+		while (context != null) {
+			if (context instanceof ConfigurableApplicationContext) {
+				ConfigurableListableBeanFactory factory = ((ConfigurableApplicationContext) context)
+						.getBeanFactory();
+				if (factory.containsBean(name)
+						&& factory.getMergedBeanDefinition(name).isPrimary()) {
+					return true;
+				}
+			}
+			context = (scope != Scope.NO_ANCESTORS) ? context.getParent() : null;
+		}
+		return false;
+	}
+
 	/**
 	 * Obtain a single bean of the given name from the application context, the bean
 	 * becoming the object under test. If no bean of the specified name can be found an

spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/context/assertj/ApplicationContextAssertTests.java

@@ -22,6 +22,10 @@ import org.junit.Test;
 
 import org.springframework.boot.test.context.assertj.ApplicationContextAssert.Scope;
 import org.springframework.context.ConfigurableApplicationContext;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.context.annotation.Primary;
 import org.springframework.context.support.StaticApplicationContext;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -244,6 +248,14 @@ public class ApplicationContextAssertTests {
 				.withMessageContaining("but found");
 	}
 
+	@Test
+	public void getBeanOfTypeWhenHasPrimaryBeanShouldReturnPrimary() {
+		AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(
+				PrimaryFooConfig.class);
+		assertThat(getAssert(context)).getBean(Foo.class).isInstanceOf(Bar.class);
+		context.close();
+	}
+
 	@Test
 	public void getBeanOfTypeWhenFailedToStartShouldFail() {
 		assertThatExceptionOfType(AssertionError.class)
@@ -423,4 +435,24 @@ public class ApplicationContextAssertTests {
 
 	}
 
+	private static class Bar extends Foo {
+
+	}
+
+	@Configuration
+	static class PrimaryFooConfig {
+
+		@Bean
+		public Foo foo() {
+			return new Foo();
+		}
+
+		@Bean
+		@Primary
+		public Bar bar() {
+			return new Bar();
+		}
+
+	}
+
 }