This document discusses good and bad properties of unit tests. It provides examples of good unit tests that are understandable, maintainable, repeatable, necessary, granular, and fast. Bad unit tests may not be understandable, maintainable, repeatable, necessary, granular, or fast. The document also discusses how to design code for testability by injecting dependencies like clocks to control test conditions. Unit tests should be treated as an executable specification and avoiding writing legacy code without tests.

1. Bad Test, Good Test
Seb Rose
Claysnow Limited
@sebrose

2. Take an index card
What makes a unit test good or bad?
- Write 3 ‘good’ things on one side
- Write 3 ‘bad’ things on the other side

3. What is a unit test?

4. Understandable

5. @Test
public 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. [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. Maintainable

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. @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. public interface CustomerBuilder {
public CustomerBuilder standardSingleMale();
public CustomerBuilder standardSingleFemale();
public CustomerBuilder smoker();
public CustomerBuilder hasOccupation(String occupation);
public Customer build();
}

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. @Test
public void smoker_requires_manual_referral()
{
Customer customer = customerBuilder
.standardSingleFemale()
.smoker()
.build();
Referral referral = underwriting.process(customer);
Assert.assertEquals(Referral.Manual, referral);
}

13. Repeatable

14. @Test
public 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. Necessary

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. Granular

18. @Test
public 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. Fast

20. Properties of unit testing
Understandable
Maintainable
Repeatable
Necessary
Granular
Fast

21. Look back at your index card
For each of your ‘good’ things, which of
the properties does it exhibit?
For each of your ‘bad’ things, which of
the properties does it contravene?

22. Have I missed any?

23. None of this is a substitute
for writing testable code.

24. class PriceCalculator {
public Price getPrice() {
if (DateTime.Compare(DateTime.Now,PRICE_RISE_DATE)<0){
return LOW_PRICE;
} else {
return HIGH_PRICE;
}
}
}

25. [Test]
public void prices_should_increase_on_2013_03_31()
{
PriceCalculator calc = new PriceCalculator();
// How can we set the date?
// ...
}

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. [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?
// ....
}

29. How can we improve?

31. Properties of unit testing
Understandable
Maintainable
Repeatable
Necessary
Granular
Fast

32. Unit tests are your executable
specification
Treat them with as much respect as
your production code

33. The Feather’s definition of legacy
code:
Code that has no tests

34. Seb Rose
Twitter:
@sebrose
Blog:
www.claysnow.co.uk
E-mail:
seb@claysnow.co.uk