[JENKINS-34855] Create a FileChannelWriter

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

@@ -0,0 +1,63 @@
+package hudson.util;
+
+import org.apache.commons.io.FileUtils;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.channels.ClosedChannelException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.StandardOpenOption;
+
+import static org.hamcrest.CoreMatchers.not;
+import static org.hamcrest.core.IsEqual.equalTo;
+import static org.junit.Assert.assertThat;
+import static org.junit.Assert.fail;
+
+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, StandardOpenOption.WRITE);
+    }
+
+    @Test
+    public void write() throws Exception {
+        writer.write("helloooo");
+        writer.close();
+
+        assertContent("helloooo");
+    }
+
+
+    @Test
+    public void flush() throws Exception {
+        writer.write("hello é è à".toCharArray());
+
+        writer.flush();
+        assertContent("hello é è à");
+    }
+
+    @Test(expected = ClosedChannelException.class)
+    public void close() throws Exception {
+        writer.write("helloooo");
+        writer.close();
+
+        writer.write("helloooo");
+        fail("Should have failed the line above");
+    }
+
+
+    private void assertContent(String string) throws IOException {
+        assertThat(FileUtils.readFileToString(file, StandardCharsets.UTF_8), equalTo(string));
+    }
+}