TestNull is a TestingPatterns.

Invoke a method with a null parameter.
If the method is not meant to be invoked with a null parameter, is
the effect of doing so documented?
Does the invocation actually have that effect?

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''Interesting point: - invoke the method with a null parameter where the method does not expect to have a null parameter, you get… guess what?, a NullPointerException. Which is the reason why NullPointerException exist? If/Where a  NullPointerException should fail you the whole application is the real question.''
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There are many ways of getting a null value when you don't want one and don't
expect one, so there's a reasonable chance that sooner or later your code will
be invoked with a bad parameter.
When this happens, it's important for your code to pass the blame onto the
calling code by acting sensibly :-).
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Isn't this better handled by assertions? 
-- abo

... assuming of course that you have a means for implementing assertions,
and that you always leave them enabled. --

No, it's better handled by exceptions. Just code as if null references couldn't happen. Most environments will throw an exception for you if you try to use a null reference, so all you have to do is handle null reference exceptions (or exceptions in general) properly and you ought to be fine. -- PhilGoodwin

Sun assert guideline says don't use assert to check parameters. http://java.sun.com/j2se/1.4.2/docs/guide/lang/assert.html#usage -- Jtf
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See also NullObject

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Keep in mind, a null pointer is not a truly bad pointer. Suppose an object's constructor assigns some global variable to this then throws an exception. I have worse schemes in my head if you want them.

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CategoryTesting CategoryNull