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Slides from my presentation at DunDDD, 17th Nov 2012.
Most of this session was spent discussing unit test examples harvested from github. If anyone would like to see them, just ask.

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1. 1. Bad Test, Good Test Seb Rose Claysnow Limited @sebrose
2. 2. Take an index cardWhat makes a unit test good or bad?- Write 3 ‘good’ things on one side- Write 3 ‘bad’ things on the other side
3. 3. What is a unit test?
4. 4. Understandable
5. 5. @Testpublic void scale() { Date now = new Date(); Calendar calBegin = Calendar.getInstance(); calBegin.setTime(now); calBegin.add(Calendar.HOUR, -4); Date begin = calBegin.getTime(); Period p = new Period(4); long delta = p.getBegin().getTime() - begin.getTime(); Assert.assertTrue( p.getEnd().compareTo(now) >= 0); logger.trace(delta); Assert.assertTrue(delta < 10 && delta > -10); Assert.assertEquals( new Integer(4), new Integer(p.getScale()));}
6. 6. [Test] public void asterisk_should_format_to_em() { // Context Formatter f = new MarkdownFormatter(); String expected = "This is <em>em</em> text"; // Action String actual = f.Format("This is *em* text"); // Outcome Assert.AreEqual(expected, actual); }
7. 7. Maintainable
8. 8. @Test public void smoker_requires_manual_referral() { Customer customer = new Customer(“Joe”, “Smith”, “12/12/1980”, “Accountant”, “\$300,000”, “Yes”, “No”); Referral referral = underwriting.process(customer); Assert.assertEquals(Referral.Manual, referral); }
9. 9. @Test public void non_smoker_does_not_require_referral() { Customer customer = new Customer(“Joe”, “Smith”, “12/12/1980”, “Accountant”, “\$300,000”, “No”, “No”); Referral referral = underwriting.process(customer); Assert.assertEquals(Referral.None, referral); }
10. 10. public interface CustomerBuilder { public CustomerBuilder standardSingleMale(); public CustomerBuilder standardSingleFemale(); public CustomerBuilder smoker(); public CustomerBuilder hasOccupation(String occupation); public Customer build();}
11. 11. @Test public void non_smoker_does_not_require_referral() { Customer customer = customerBuilder .standardSingleMale() .build(); Referral referral = underwriting.process(customer); Assert.assertEquals(Referral.None, referral); }
12. 12. @Test public void smoker_requires_manual_referral() { Customer customer = customerBuilder .standardSingleFemale() .smoker() .build(); Referral referral = underwriting.process(customer); Assert.assertEquals(Referral.Manual, referral); }
13. 13. Repeatable
14. 14. @Testpublic void testRolling() { Yahtzee y = Yahtzee.roll(); assertEquals(y, y); Yahtzee y1 = new Yahtzee(1,2,3,4,5); Yahtzee y2 = new Yahtzee(1,2,3,4,5); assertTrue(y1.equals(y2)); assertEquals(y1,y2); assertFalse(Yahtzee.roll()==Yahtzee.roll());}
15. 15. Necessary
16. 16. [Test]#region TestCase...public void TestMapFromRomanNormalToRomanOnes( string roman, int times){ var actual = _engine.ToRomanOnes(roman); var expected = _engine.Repeat(I, times); Assert.That(actual, Is.EqualTo(expected));}
17. 17. Granular
18. 18. @Testpublic void testRolling() { Yahtzee y = Yahtzee.roll(); assertEquals(y, y); Yahtzee y1 = new Yahtzee(1,2,3,4,5); Yahtzee y2 = new Yahtzee(1,2,3,4,5); assertTrue(y1.equals(y2)); assertEquals(y1,y2); assertFalse(Yahtzee.roll()==Yahtzee.roll());}
19. 19. Fast
20. 20. Properties of unit testing Understandable Maintainable Repeatable Necessary Granular Fast
21. 21. Look back at your index cardFor each of your ‘good’ things, which ofthe properties does it exhibit?For each of your ‘bad’ things, which ofthe properties does it contravene?
22. 22. Have I missed any?
23. 23. None of this is a substitute for writing testable code.
24. 24. class PriceCalculator { public Price getPrice() { if (DateTime.Compare(DateTime.Now,PRICE_RISE_DATE)<0){ return LOW_PRICE; } else { return HIGH_PRICE; } }}
25. 25. [Test] public void prices_should_increase_on_2013_03_31() { PriceCalculator calc = new PriceCalculator(); // How can we set the date? // ... }
26. 26. class PriceCalculator { public PriceCalculator( SystemClock clock ) { clock_ = clock; } public Price getPrice() { if (DateTime.Compare(clock.Now, PRICE_RISE_DATE)<0){ return LOW_PRICE; } else { return HIGH_PRICE; } }}
27. 27. [Test] public void prices_should_increase_on_2013_03_31() { SystemClock clock = new SystemClock(2013, 03, 31); PriceCalculator calc = new PriceCalculator(clock); // Now we control the date? // .... }
28. 28. How can we improve?
29. 29. Properties of unit testing Understandable Maintainable Repeatable Necessary Granular Fast
30. 30. Unit tests are your executable speciﬁcationTreat them with as much respect as your production code
31. 31. The Feather’s deﬁnition of legacycode: Code that has no tests
32. 32. Seb RoseTwitter: @sebroseBlog: www.claysnow.co.ukE-mail: seb@claysnow.co.uk