bad test, good test
DESCRIPTION
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.TRANSCRIPT
Bad Test, Good Test
Seb RoseClaysnow Limited
@sebrose
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
What is a unit test?
Understandable
@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())); }
[Test] public void asterisk_should_format_to_em() {
// ContextFormatter f = new MarkdownFormatter();String expected = "This is <em>em</em> text";
// ActionString actual = f.Format("This is *em* text");
// OutcomeAssert.AreEqual(expected, actual);
}
Maintainable
@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); }
@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); }
public interface CustomerBuilder {public CustomerBuilder standardSingleMale();public CustomerBuilder standardSingleFemale();
public CustomerBuilder smoker();public CustomerBuilder hasOccupation(String occupation);
public Customer build();}
@Test public void non_smoker_does_not_require_referral() {
Customer customer = customerBuilder.standardSingleMale().build();
Referral referral = underwriting.process(customer);
Assert.assertEquals(Referral.None, referral); }
@Test public void smoker_requires_manual_referral() {
Customer customer = customerBuilder.standardSingleFemale().smoker().build();
Referral referral = underwriting.process(customer);
Assert.assertEquals(Referral.Manual, referral); }
Repeatable
@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()); }
Necessary
[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));}
Granular
@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()); }
Fast
Properties of unit testing
UnderstandableMaintainableRepeatableNecessaryGranular
Fast
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?
Have I missed any?
None of this is a substitutefor writing testable code.
class PriceCalculator {public Price getPrice() {
if (DateTime.Compare(DateTime.Now,PRICE_RISE_DATE)<0){return LOW_PRICE;
} else {return HIGH_PRICE;
}}
}
[Test] public void prices_should_increase_on_2013_03_31() {
PriceCalculator calc = new PriceCalculator();
// How can we set the date?// ...
}
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;}
}}
[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?// ....
}
How can we improve?
Properties of unit testing
UnderstandableMaintainableRepeatableNecessaryGranular
Fast
Unit tests are your executable specification
Treat them with as much respect as your production code
The Feather’s definition of legacy code:
Code that has no tests
