# Testowanie oparte na właściwościach

## Magda Stożek

``BigDecimal calculateDiscount(Customer customer, LocalDate now);``

Staż:

0-1

1-2

2 +

0%

30%

10%

20%

urodziny

``````class Customer {
private final String name;
private final LocalDate joinedAt;
private final LocalDate dateOfBirth;
// (...)
}``````
``````@Test
void shouldCalculate10percentDiscount() {
LocalDate now = LocalDate.of(2019, 9, 15);
LocalDate dateOfBirth = LocalDate.of(1980, 1, 20);
Customer customer = new Customer("Sue Smith", now.minusYears(1), dateOfBirth);

BigDecimal discount = calculator.calculateDiscount(customer, now);

Assertions.assertThat(discount).isEqualTo(new BigDecimal("0.1"));
}

@Test
void shouldCalculate20percentDiscount() {
LocalDate now = LocalDate.of(2019, 9, 15);
LocalDate dateOfBirth = LocalDate.of(1980, 1, 20);
Customer customer = new Customer("Sue Smith", now.minusYears(2), dateOfBirth);

BigDecimal discount = calculator.calculateDiscount(customer, now);

Assertions.assertThat(discount).isEqualTo(new BigDecimal("0.2"));
}
``````

### Testy oparte na przykładach

``````@Test
void shouldCalculateBirthdayDiscount() {
Customer customer = new Customer("Sue Smith", NOW, NOW.withYear(1980));

BigDecimal discount = calculator.calculateDiscount(customer, NOW);

Assertions.assertThat(discount).isEqualTo(new BigDecimal("0.3"));
}``````
``````@Test
void shouldCalculateNoDiscount() {
Customer customer = new Customer("Sue Smith", NOW, LocalDate.of(1980, 1, 20));

BigDecimal discount = calculator.calculateDiscount(customer, NOW);

Assertions.assertThat(discount).isEqualTo(new BigDecimal("0"));
}

@Test
void shouldCalculate20percentDiscountFor3Years() {
LocalDate now = LocalDate.of(2019, 9, 15);
LocalDate dateOfBirth = LocalDate.of(1980, 1, 20);
Customer customer = new Customer("Sue Smith", now.minusYears(3), dateOfBirth);

BigDecimal discount = calculator.calculateDiscount(customer, now);

Assertions.assertThat(discount).isEqualTo(new BigDecimal("0.2"));
}
``````

# A w języku właściwości?

``BigDecimal calculateDiscount(Customer customer, LocalDate now);``

Staż:

0-1

1-2

2 +

0%

30%

10%

20%

urodziny

``````class Customer {
private final String name;
private final LocalDate joinedAt;
private final LocalDate dateOfBirth;
// (...)
}``````

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## Co dla Javy?

``````@Property
boolean discountShouldNotBeOver30percent(@ForAll("validCustomer") Customer customer, @ForAll("futureDate") LocalDate now) {

BigDecimal discount = calculator.calculateDiscount(customer, now);
return discount.compareTo(new BigDecimal("0.3")) <= 0;
}``````

Właściwość: zniżka nigdy nie przekracza 30%

``````                              |-------------------jqwik-------------------
tries = 374                   | # of calls to property
checks = 374                  | # of not rejected calls
generation-mode = RANDOMIZED  | parameters are randomly generated
after-failure = PREVIOUS_SEED | use the previous seed
seed = -272292185905571017    | random seed to reproduce generated values
sample =
[Customer{name='AAA', joinedAt=2010-01-01, dateOfBirth=1980-02-29}, 2019-10-06]
original-sample =
[Customer{name='DtQDpPfEx', joinedAt=2010-04-21, dateOfBirth=1980-02-29}, 2185-03-17]
``````

Wykryty błąd

# Generatory

``````@ForAll String sentence

@ForAll @StringLength(min = 3, max = 100) String sentence

@ForAll @AlphaChars @NumericChars @Chars({',', '.', ':', ';', '-'}) @Whitespace String sentence
``````

Tekstowe

``````@ForAll Integer number

@ForAll @Positive Integer number

@ForAll @BigRange(min = "1", max = "99.99") @Scale(2) BigDecimal price``````

Liczbowe

``````@ForAll List<@Alpha String> words

@ForAll @Size(10) Set<@Negative Integer> numbers
``````

Kolekcje

``````@ForAll Optional<String> middleName

@ForAll @WithNull String middleName``````

Optional

``````@Property
boolean myProperty(@ForAll("shortStrings") String string, @ForAll("10 to 99") int number) {
String concatenated = string + number;
return concatenated.length() > 2 && concatenated.length() < 11;
}

@Provide
Arbitrary<String> shortStrings() {
return Arbitraries.strings().withCharRange('a', 'z').filter('q')
.ofMinLength(1).ofMaxLength(8);
}

@Provide("10 to 99")
Arbitrary<Integer> numbers() {
return Arbitraries.integers().between(10, 99);
}``````

Własne generatory

``````@Property
boolean discountShouldNotBeOver30percent(@ForAll("validCustomer") Customer customer) {
BigDecimal discount = calculator.calculateDiscount(customer);
return discount.compareTo(new BigDecimal("0.3")) <= 0;
}

@Provide
Arbitrary<Customer> validCustomer() {
Arbitrary<String> names = Arbitraries.strings().alpha().ofMinLength(3).ofMaxLength(21);
Arbitrary<LocalDate> joined = datesGen(BUSINESS_START, LocalDate.now());
Arbitrary<LocalDate> born = datesGen(MIN_DOB, LocalDate.now().minusYears(18));
return Combinators.combine(names, joined, born).as(Customer::new);
}

Arbitrary<LocalDate> datesGen(LocalDate minDate, LocalDate maxDate) {
long range = DAYS.between(minDate, maxDate);
return Arbitraries.longs().between(0, range).map(n -> minDate.plus(n, DAYS));
}``````

``````@Property
boolean discountShouldBeProportionalToMembershipYears(@ForAll Customer older, @ForAll Customer newer) {
Assume.that(isNotBirthday(older, now));

BigDecimal discountForOlderCustomer = calculator.calculateDiscount(older);
return discountForOlderCustomer.compareTo(discountForNewerCustomer) >= 0;
}``````

Zawężenia

``````class MyCustomerArbitraryProvider implements ArbitraryProvider {
@Override
public boolean canProvideFor(TypeUsage targetType) { (...) }

@Override
public Set<Arbitrary<?>> provideFor(TypeUsage targetType, SubtypeProvider subtypeProvider) { (...) }
}``````

Domyślne generatory

META-INF/services/net.jqwik.api.providers.ArbitraryProvider:

``pbt.MyCustomerArbitraryProvider``
``@ForAll("validCustomer") Customer customer``
``@ForAll Customer customer``
``````@Property
void shouldCalculateDiscount(@ForAll("membershipYears") Short years) {
BigDecimal discount = calculator.prepareDiscount(years);
//(...)
}

@Provide
Arbitrary<Short> membershipYears() {
return Arbitraries.frequency(
Tuple.of(30, 0),
Tuple.of(60, 1),
Tuple.of(7, 2),
Tuple.of(3, 3)
);
}``````

Częstotliwości

# Wyzwania

Wyzwanie #1

Wyzwanie #2

(Oracle)

## Alternatywne sformułowanie

(Alternate wording)

(Invariants)

(Symmetry)

Wyzwanie #3

Wyzwanie #4

# Strategie

• najpierw przykłady, potem właściwości
• właściwości dla kluczowych elementów

# Podsumowanie

• większy koszt, większa korzyść
• przypadki brzegowe i luki w rozumowaniu
• wymyślanie właściwości
• proporcje

## Więcej

### Pytania?

``````@Property
boolean endOfPresentation(@ForAll Attendee attendee) {
Assume.that(attendee.hasQuestions());

return attendee.questionsAsked > 0;
}``````

By Magda Stożek

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