Align TransactionManagementConfigurer support in TCF with production

This commit picks up where 613bd3be1d
left off by ensuring that a transaction manager configured via the
TransactionManagementConfigurer API takes precedence over any
transaction manager configured as a bean in the ApplicationContext
unless @Transactional is configured with a qualifier for the explicit
transaction manager to use in tests.

Closes gh-24869

spring-test/src/test/java/org/springframework/test/context/transaction/manager/LookUpTxMgrViaTransactionManagementConfigurerWithSingleTxMgrBeanTests.java

@@ -0,0 +1,99 @@
+/*
+ * Copyright 2002-2020 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.test.context.transaction.manager;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
+import org.springframework.test.context.transaction.AfterTransaction;
+import org.springframework.transaction.TransactionManager;
+import org.springframework.transaction.annotation.TransactionManagementConfigurer;
+import org.springframework.transaction.annotation.Transactional;
+import org.springframework.transaction.testfixture.CallCountingTransactionManager;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Integration test that verifies the behavior for transaction manager lookups
+ * when only one transaction manager is configured as a bean in the application
+ * context and a non-bean transaction manager is configured via the
+ * {@link TransactionManagementConfigurer} API.
+ *
+ * @author Sam Brannen
+ * @since 5.3
+ */
+@SpringJUnitConfig
+@Transactional
+class LookUpTxMgrViaTransactionManagementConfigurerWithSingleTxMgrBeanTests {
+
+	@Autowired
+	CallCountingTransactionManager txManager;
+
+	@Autowired
+	Config config;
+
+
+	@Test
+	void transactionalTest() {
+		assertThat(txManager.begun).isEqualTo(0);
+		assertThat(txManager.inflight).isEqualTo(0);
+		assertThat(txManager.commits).isEqualTo(0);
+		assertThat(txManager.rollbacks).isEqualTo(0);
+
+		CallCountingTransactionManager annotationDriven = config.annotationDriven;
+		assertThat(annotationDriven.begun).isEqualTo(1);
+		assertThat(annotationDriven.inflight).isEqualTo(1);
+		assertThat(annotationDriven.commits).isEqualTo(0);
+		assertThat(annotationDriven.rollbacks).isEqualTo(0);
+	}
+
+	@AfterTransaction
+	void afterTransaction() {
+		assertThat(txManager.begun).isEqualTo(0);
+		assertThat(txManager.inflight).isEqualTo(0);
+		assertThat(txManager.commits).isEqualTo(0);
+		assertThat(txManager.rollbacks).isEqualTo(0);
+
+		CallCountingTransactionManager annotationDriven = config.annotationDriven;
+		assertThat(annotationDriven.begun).isEqualTo(1);
+		assertThat(annotationDriven.inflight).isEqualTo(0);
+		assertThat(annotationDriven.commits).isEqualTo(0);
+		assertThat(annotationDriven.rollbacks).isEqualTo(1);
+	}
+
+
+	@Configuration
+	static class Config implements TransactionManagementConfigurer {
+
+		final CallCountingTransactionManager annotationDriven = new CallCountingTransactionManager();
+
+		@Bean
+		TransactionManager txManager() {
+			return new CallCountingTransactionManager();
+		}
+
+		@Override
+		public TransactionManager annotationDrivenTransactionManager() {
+			return annotationDriven;
+		}
+
+	}
+
+}