Add support for merging two BeanRegistrationAotContribution instances

Closes gh-31446

spring-beans/src/test/java/org/springframework/beans/factory/aot/BeanRegistrationAotContributionTests.java

@@ -0,0 +1,70 @@
+/*
+ * Copyright 2002-2023 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.beans.factory.aot;
+
+import org.junit.jupiter.api.Test;
+import org.mockito.InOrder;
+
+import org.springframework.aot.test.generate.TestGenerationContext;
+import org.springframework.beans.testfixture.beans.factory.aot.MockBeanRegistrationCode;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.inOrder;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verifyNoInteractions;
+
+/**
+ * Tests for {@link BeanRegistrationAotContribution}.
+ *
+ * @author Stephane Nicoll
+ */
+class BeanRegistrationAotContributionTests {
+
+	@Test
+	void concatWithBothNullReturnsNull() {
+		assertThat(BeanRegistrationAotContribution.concat(null, null)).isNull();
+	}
+
+	@Test
+	void concatWithFirstNullReturnsSecondAsIs() {
+		BeanRegistrationAotContribution contribution = mock(BeanRegistrationAotContribution.class);
+		assertThat(BeanRegistrationAotContribution.concat(null, contribution)).isSameAs(contribution);
+		verifyNoInteractions(contribution);
+	}
+
+	@Test
+	void concatWithSecondNullReturnsFirstAsIs() {
+		BeanRegistrationAotContribution contribution = mock(BeanRegistrationAotContribution.class);
+		assertThat(BeanRegistrationAotContribution.concat(contribution, null)).isSameAs(contribution);
+		verifyNoInteractions(contribution);
+	}
+
+	@Test
+	void concatApplyContributionsInOrder() {
+		BeanRegistrationAotContribution first = mock(BeanRegistrationAotContribution.class);
+		BeanRegistrationAotContribution second = mock(BeanRegistrationAotContribution.class);
+		BeanRegistrationAotContribution combined = BeanRegistrationAotContribution.concat(first, second);
+		assertThat(combined).isNotNull();
+		TestGenerationContext generationContext = new TestGenerationContext();
+		BeanRegistrationCode beanRegistrationCode = new MockBeanRegistrationCode(generationContext);
+		combined.applyTo(generationContext, beanRegistrationCode);
+		InOrder ordered = inOrder(first, second);
+		ordered.verify(first).applyTo(generationContext, beanRegistrationCode);
+		ordered.verify(second).applyTo(generationContext, beanRegistrationCode);
+	}
+
+}