Polish ConcurrentBeanWrapperTests

spring-beans/src/test/java/org/springframework/beans/ConcurrentBeanWrapperTests.java

 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -18,18 +18,16 @@ package org.springframework.beans;
 
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
-import java.util.Collections;
-import java.util.HashSet;
 import java.util.Iterator;
 import java.util.Properties;
 import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.junit.jupiter.api.RepeatedTest;
 import org.junit.jupiter.api.Test;
 
-
 import static org.assertj.core.api.Assertions.assertThat;
 
 /**
@@ -38,21 +36,21 @@ import static org.assertj.core.api.Assertions.assertThat;
  * @author Chris Beams
  * @since 08.03.2004
  */
-public class ConcurrentBeanWrapperTests {
+class ConcurrentBeanWrapperTests {
 
 	private final Log logger = LogFactory.getLog(getClass());
 
-	private Set<TestRun> set = Collections.synchronizedSet(new HashSet<TestRun>());
+	private final Set<TestRun> set = ConcurrentHashMap.newKeySet();
 
 	private Throwable ex = null;
 
 	@RepeatedTest(100)
-	public void testSingleThread() {
+	void testSingleThread() {
 		performSet();
 	}
 
 	@Test
-	public void testConcurrent() {
+	void testConcurrent() {
 		for (int i = 0; i < 10; i++) {
 			TestRun run = new TestRun(this);
 			set.add(run);
@@ -82,7 +80,7 @@ public class ConcurrentBeanWrapperTests {
 
 		Properties p = (Properties) System.getProperties().clone();
 
-		assertThat(p.size() != 0).as("The System properties must not be empty").isTrue();
+		assertThat(p).as("The System properties must not be empty").isNotEmpty();
 
 		for (Iterator<?> i = p.entrySet().iterator(); i.hasNext();) {
 			i.next();
@@ -111,7 +109,7 @@ public class ConcurrentBeanWrapperTests {
 
 		private ConcurrentBeanWrapperTests test;
 
-		public TestRun(ConcurrentBeanWrapperTests test) {
+		TestRun(ConcurrentBeanWrapperTests test) {
 			this.test = test;
 		}