JUnit 3 test runners invoke the setUp() method before running each test. 
For example, from XOM:
protected void setUp() {
        
    System.setErr(new PrintStream(new ByteArrayOutputStream()));
        
    inputDir = new File("data");
    inputDir = new File(inputDir, "xslt");
    inputDir = new File(inputDir, "input");
        
}Each setUp() method is supposed to invoke its superclass's setUp() method, but this is often forgotten