Bad test, good test

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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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  • Untestable code. Test first/TDD
  • Naming Locality of reference Symbolic constants Distinguish Context/Action/Outcome Documentation - writing for other developers NOT the compiler
  • Symbolic constant
  • Naming Locality Context/Action/Outcome
  • Abstractions White box (TDD) but not mirroring implementation SOLID - DRY
  • Data
  • Data
  • Builders/Data DRY Can build graphs
  • Builders
  • Builders
  • No unreliable resources file system/network No dates/random numbers
  • Triangulation
  • What’s this for?
  • Single behaviour CHeck back to naming Executable Documentation
  • No unreliable resources file system/network No dates/random numbers
  • Osherove - maintainable, trustworthy, readable Bache - coverage, readability, robustness, speed
  • TDD. Decoupling.
  • Bad test, good test

    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

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