Fix incomplete assertions

Closes gh-30209

spring-core/src/test/java/org/springframework/core/io/ClassPathResourceTests.java

@@ -231,7 +231,7 @@ class ClassPathResourceTests {
 	void emptyFileReadable(@TempDir(cleanup = NEVER) File tempDir) throws IOException {
 		File file = new File(tempDir, "empty.txt");
 		assertThat(file.createNewFile()).isTrue();
-		assertThat(file.isFile());
+		assertThat(file.isFile()).isTrue();
 
 		try (URLClassLoader fileClassLoader = new URLClassLoader(new URL[]{tempDir.toURI().toURL()})) {
 			Resource emptyFile = new ClassPathResource("empty.txt", fileClassLoader);
@@ -246,7 +246,7 @@ class ClassPathResourceTests {
 			zipOut.putNextEntry(new ZipEntry("empty2.txt"));
 			zipOut.closeEntry();
 		}
-		assertThat(jarFile.isFile());
+		assertThat(jarFile.isFile()).isTrue();
 
 		try (URLClassLoader jarClassLoader = new URLClassLoader(new URL[]{jarFile.toURI().toURL()})) {
 			Resource emptyJarEntry = new ClassPathResource("empty2.txt", jarClassLoader);

spring-messaging/src/test/java/org/springframework/messaging/simp/stomp/DefaultStompSessionTests.java

@@ -398,7 +398,7 @@ public class DefaultStompSessionTests {
 	@Test // gh-23358
 	public void sendByteArray() {
 		this.session.afterConnected(this.connection);
-		assertThat(this.session.isConnected());
+		assertThat(this.session.isConnected()).isTrue();
 
 		String destination = "/topic/foo";
 		String payload = "sample payload";

spring-messaging/src/test/java/org/springframework/messaging/support/NativeMessageHeaderAccessorTests.java

@@ -236,7 +236,7 @@ public class NativeMessageHeaderAccessorTests {
 		Message<?> target = MessageBuilder.createMessage(source.getPayload(), targetAccessor.getMessageHeaders());
 
 		MessageHeaderAccessor accessor = MessageHeaderAccessor.getMutableAccessor(target);
-		assertThat(accessor.isMutable());
+		assertThat(accessor.isMutable()).isTrue();
 		((NativeMessageHeaderAccessor) accessor).addNativeHeader("foo", "baz");
 		assertThat(((NativeMessageHeaderAccessor) accessor).getNativeHeader("foo")).containsExactly("bar", "baz");
 	}
@@ -253,7 +253,7 @@ public class NativeMessageHeaderAccessorTests {
 		Message<?> target = MessageBuilder.createMessage(source.getPayload(), targetAccessor.getMessageHeaders());
 
 		MessageHeaderAccessor accessor = MessageHeaderAccessor.getMutableAccessor(target);
-		assertThat(accessor.isMutable());
+		assertThat(accessor.isMutable()).isTrue();
 		((NativeMessageHeaderAccessor) accessor).addNativeHeader("foo", "baz");
 		assertThat(((NativeMessageHeaderAccessor) accessor).getNativeHeader("foo")).containsExactly("bar", "baz");
 	}