Use assertThat from Hamcrest instead of JUnit 4

org.junit.Assert.assertThat() is deprecated as of JUnit 4.13.

See gh-22894

spring-tx/src/test/java/org/springframework/transaction/TxNamespaceHandlerEventTests.java

@@ -27,7 +27,7 @@ import org.springframework.core.io.ClassPathResource;
 import org.springframework.tests.beans.CollectingReaderEventListener;
 
 import static org.hamcrest.CoreMatchers.*;
-import static org.junit.Assert.*;
+import static org.hamcrest.MatcherAssert.assertThat;
 
 /**
  * @author Torsten Juergeleit

spring-tx/src/test/java/org/springframework/transaction/annotation/EnableTransactionManagementTests.java

@@ -39,6 +39,7 @@ import org.springframework.transaction.config.TransactionManagementConfigUtils;
 import org.springframework.transaction.event.TransactionalEventListenerFactory;
 
 import static org.hamcrest.CoreMatchers.*;
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.junit.Assert.*;
 
 /**

spring-tx/src/test/java/org/springframework/transaction/interceptor/RollbackRuleTests.java

@@ -23,6 +23,7 @@ import org.junit.Test;
 import org.springframework.beans.FatalBeanException;
 
 import static org.hamcrest.CoreMatchers.*;
+import static org.hamcrest.MatcherAssert.assertThat;
 import static org.junit.Assert.*;
 
 /**