Fix chackstyle violations in test

See gh-18012

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/web/context/WebServerApplicationContextTests.java

@@ -16,7 +16,7 @@
 
 package org.springframework.boot.web.context;
 
-import org.junit.Test;
+import org.junit.jupiter.api.Test;
 
 import org.springframework.context.ApplicationContext;
 
@@ -32,19 +32,19 @@ import static org.mockito.Mockito.mock;
 public class WebServerApplicationContextTests {
 
 	@Test
-	public void hasServerNamespaceWhenContextIsNotWebServerApplicationContextReturnsFalse() {
+	void hasServerNamespaceWhenContextIsNotWebServerApplicationContextReturnsFalse() {
 		ApplicationContext context = mock(ApplicationContext.class);
 		assertThat(WebServerApplicationContext.hasServerNamespace(context, "test")).isFalse();
 	}
 
 	@Test
-	public void hasServerNamespaceWhenContextIsWebServerApplicationContextAndNamespaceDoesNotMatchReturnsFalse() {
+	void hasServerNamespaceWhenContextIsWebServerApplicationContextAndNamespaceDoesNotMatchReturnsFalse() {
 		ApplicationContext context = mock(WebServerApplicationContext.class);
 		assertThat(WebServerApplicationContext.hasServerNamespace(context, "test")).isFalse();
 	}
 
 	@Test
-	public void hasServerNamespaceWhenContextIsWebServerApplicationContextAndNamespaceMatchesReturnsTrue() {
+	void hasServerNamespaceWhenContextIsWebServerApplicationContextAndNamespaceMatchesReturnsTrue() {
 		WebServerApplicationContext context = mock(WebServerApplicationContext.class);
 		given(context.getServerNamespace()).willReturn("test");
 		assertThat(WebServerApplicationContext.hasServerNamespace(context, "test")).isTrue();