IOException Test Demo

import java.io.*;
/**
 * Demo of how to test that an IOException is being caught correctly.
 * Low level read operations can throw IOException.
 * If you use scanner, this won't happen.
 */
public class TestIOException extends junit.framework.TestCase
{
    // Return false if write attempt fails
    private boolean write(FileOutputStream out)
    {
        boolean result = true;
        try
        {
            out.write (new byte[3]);
        }
        catch (IOException ex)
        {
            result = false;
        }
        return result;
    }

    public void testWrite() throws IOException
    {
        // Fake stream always throws IOException
        MyFakeStream out = new MyFakeStream("XYZ");
        assertFalse(write(out));
    }

}

import java.io.*;
/** A mock output stream that will ALWAYS throw IOException when writing.
 * @author jdalbey
 * @version 0.1
 */
public class MyFakeStream extends FileOutputStream
{
    public MyFakeStream (String filename) throws IOException
    {
        super (getFDOf (filename));
    }

    @Override
    public void write(byte[] b) throws IOException
    {
        throw new IOException();
    }

    protected static FileDescriptor getFDOf (String filename) throws IOException
    {
         RandomAccessFile file = new RandomAccessFile (filename, "rw");
         return file.getFD ();
    }
}