Testing outputstream.write(<String>) without creating a file

Question

I am testing a output stream in java something like below.

    Writer outputStream = getOutputStream(fileName);
    if(outputStream != null) {
        try {
            outputStream.write(inputText);
        }
        finally {
            outputStream.close();
        }
    }
    else {
        throw new IOException("Output stream is null");
    }

I am write a mockito test as below

public void testFileWrite() throws IOException {
    when(testObj.getOutputStream(outputFileNameValidValue)).thenReturn(outputStreamMock);
    doNothing().when(outputStreamMock).write(Matchers.anyString());
    doNothing().when(bufferedReaderMock).close();

    testObj.write(outputFileNameValidValue, reveredFileInput);

    verify(outputStreamMock).write(Matchers.anyString());
    verify(outputStreamMock).close();
}

The problem is when you create OutputStreamWriter(new FileOutputStream(filename)) a physical file on the disk is created.

Can we test Outputstream.write without actually writing a file on the disk?

Thanks Anand

Answer 1

You can use ByteArrayOutputStream which writes the data in memory. You can read this with a ByteArrayInputStream.

An alternative is to write an expecting OutputStream which fails as soon as you attempt to write an incorrect byte. This can be helpful to see exactly where/why a test fails.

Answer 2

You could try using System.out for your output which is actually a Printstream, which is a subclass of OutputStream

see: http://docs.oracle.com/javase/6/docs/api/java/lang/System.html http://docs.oracle.com/javase/6/docs/api/java/io/PrintStream.html