Fix FileChannelWriterTest and VirtualFileTest for JUnit 5 (#10713)

Author: strangelookingnerd

core/src/test/java/hudson/util/FileChannelWriterTest.java

@@ -2,59 +2,53 @@
 
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.Matchers.equalTo;
-import static org.junit.Assert.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 
-import java.io.File;
 import java.io.IOException;
 import java.nio.channels.ClosedChannelException;
 import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
+import java.nio.file.Path;
 import java.nio.file.StandardOpenOption;
-import org.junit.Before;
-import org.junit.Rule;
-import org.junit.Test;
-import org.junit.rules.TemporaryFolder;
-
-public class FileChannelWriterTest {
-    @Rule
-    public TemporaryFolder temporaryFolder = new TemporaryFolder();
-
-    File file;
-    FileChannelWriter writer;
-
-    @Before
-    public void setUp() throws Exception {
-        file = temporaryFolder.newFile();
-        writer = new FileChannelWriter(file.toPath(), StandardCharsets.UTF_8, true, true,  StandardOpenOption.WRITE);
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+class FileChannelWriterTest {
+
+    private Path file;
+    private FileChannelWriter writer;
+
+    @BeforeEach
+    void setUp() throws Exception {
+        file = Files.createTempFile("junit", null);
+        writer = new FileChannelWriter(file, StandardCharsets.UTF_8, true, true,  StandardOpenOption.WRITE);
     }
 
     @Test
-    public void write() throws Exception {
+    void write() throws Exception {
         writer.write("helloooo");
         writer.close();
 
         assertContent("helloooo");
     }
 
-
     @Test
-    public void flush() throws Exception {
+    void flush() throws Exception {
         writer.write("hello é è à".toCharArray());
 
         writer.flush();
         assertContent("hello é è à");
     }
 
     @Test
-    public void close() throws Exception {
+    void close() throws Exception {
         writer.write("helloooo");
         writer.close();
 
         assertThrows(ClosedChannelException.class, () -> writer.write("helloooo"));
     }
 
-
     private void assertContent(String string) throws IOException {
-        assertThat(Files.readString(file.toPath(), StandardCharsets.UTF_8), equalTo(string));
+        assertThat(Files.readString(file, StandardCharsets.UTF_8), equalTo(string));
     }
 }