public void testNullInputGivesCorrectErrorMessage() throws MalformedParenthesisException, InvalidOperandException, MalformedTokenException, MalformedDecimalException {
		
		String badExpressionString = null;
		
		try {
		
			Expression badExpression = new Expression(badExpressionString);
			fail("Expression not thrown!?");
		} catch (IllegalArgumentException e) {
			
			assertEquals(e.getLocalizedMessage(), Expression.illegalArgString);
		}
	}