Testing what's written to a Java OutputStream

Question

I am about to write junit tests for a XML parsing Java class that outputs directly to an OutputStream. For example xmlWriter.writeString(\"foo\"); would produce

Answer 1

It's simple. As @JonSkeet said:

ByteArrayOutputStream baos = new ByteArrayOutputStream();
// pass the baos to be writed with "value", for this example
byte[] byteArray = baos.toByteArray();
Assert.assertEquals("value", new String(byteArray));

Answer 2

Use a ByteArrayOutputStream and then get the data out of that using toByteArray(). This won't test how it writes to the stream (one byte at a time or as a big buffer) but usually you shouldn't care about that anyway.

Answer 3

If you can pass a Writer to XmlWriter, I would pass it a StringWriter. You can query the StringWriter's contents using toString() on it.

If you have to pass an OutputStream, you can pass a ByteArrayOutputStream and you can also call toString() on it to get its contents as a String.

Then you can code something like:

public void testSomething()
{
  Writer sw = new StringWriter();
  XmlWriter xw = new XmlWriter(sw);
  ...
  xw.writeString("foo");
  ...
  assertEquals("...<aTag>foo</aTag>...", sw.toString());
}