source: class SequentialReceiptNumberGeneratorTest {
  
  	private ISequentialReceiptNumberGeneratorService service;
  	private SequentialReceiptNumberGenerator generator;
  	private Calendar calendar;
  
  	@Test(expected = NullPointerException.class)
  	public void generateNumber_shouldThrowNullPointerExceptionIfBillIsNull() throws Exception {
  
target: 		generator.generateNumber(null);
  	}
  
  }