developer tests - things to know
Post on 15-Jul-2015
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meMy hobbies● developer at Wix.com● main language - Scala● main professional interest - developer communities
If there is time left after my hobbies● mountain bicycle rider, snowboarder ● consumer of rock music, contemporary art, etc
me - how to contact meconnect with me on LinkedIn http://lt.linkedin.com/pub/vaidas-pilkauskas/8/77/863/
add me on G+ https://www.google.com/+VaidasPilkauskas
follow on Twitter @liucijus
“We couldn’t understand why people without technical knowledge had to tell programmers “what” to do and, furthermore, they had to supervise “how” programmers did it.”
Cristian Rennellahttp://qz.com/260846/why-our-startup-has-no-bosses-no-office-and-a-four-day-work-week/
What this talk is about
● Things we argue about during code reviews● Things that took me time to understand and
prove that they are actually good way to go● Small things we have no time to discuss
during big talks
So what is test?
It is system’s exercise under predefined conditions and then verification of an expected outcome.
Test structure
http://healthysimulation.com/2743/structure-collapse-simulator-constructed-by-strategic-response-initiatives/
Test phases in code Server server = new NotesServer(); // setup
Note note = new Note("test note"); // setup
Status status = server.add(note); // exercise
assertEquals(SUCCESS, status); // verify
server.shutdown(); // teardown
Start everything in one method@Test
public void serverShouldAddNoteSuccessfully() {
Server server = new NotesServer(); // setup
Note note = new Note("test note"); // setup
Status status = server.add(note); // exercise
assertEquals(SUCCESS, status); // verify
server.shutdown(); // teardown
}
Refactor to lifecycle methods@Before public void before() {
server = new NotesServer(); // setup
note = new Note("test note"); // setup
}
@Test public void serverShouldAddNoteSuccessfully() {
Status status = server.add(note); // exercise
assertEquals(SUCCESS, status); // verify
}
@After public void after() {
server.shutdown(); // teardown
}
@Test public void shouldServeEmptyUserList() { server.start(); assertThat(server.getUsers(), is(empty())); server.stop();}
@Before public void startServer() { server.start();}
@Test public void shouldServeEmptyUserList() {
//todo: implement
}
@After public void stopServer() { server.stop();}
BAD
GOOD
Let’s talk about setup in @Before@Before public void before() {
server = new NotesServer(); // setup
note = new Note("test note"); // setup
}
@Test public void serverShouldAddNoteSuccessfully() {
Status status = server.add(note); // exercise
assertEquals(SUCCESS, status); // verify
}
@After public void after() { server.shutdown(); // teardown }
BAD@Before public void preparePets() {
cat = new Cat(); // only needed by dogShouldSayFoo
dog = new Dog(); // only needed by catShouldSayBar
}
@Test public void dogShouldSayFoo() {
assertThat(dog.says(), is("foo"))
}
@Test public void catShouldSayBar() {
assertThat(cat.says(), is("bar"))
}
BAD@Before public void preparePets() {
cat = new Cat().withHairstyle(CURLY);
dog = new Dog();
}
@Test public void curlyCatShouldFeelBeautiful(){
assertThat(cat.isFeelingBeautiful(), is(true));
}
@Test public void dogShouldSayFoo() {
assertThat(dog.says(), is("foo"));
}
@Test public void catShouldSayBar() {
assertThat(cat.says(), is("bar"));
}
Setting up note inside test method@Before public void before() {
server = new NotesServer(); // setup
}
@Test public void serverShouldAddNoteSuccessfully() {
note = new Note("test note"); // setup
Status status = server.add(note); // exercise
assertEquals(SUCCESS, status); // verify
}
But then be more specific@Test
public void serverShouldAddSingleLineNoteSuccesfully() {
// * set up which is actual for the current method
// * use scope specific name
Note singleLineNote = new Note("test note"); // setup
Status status = server.add(singleLineNote); // exercise
assertEquals(SUCCESS, status); // verify
}
Give good names to setup methods
@Before public void createNotesServer() { server = new NotesServer(); }
Summary of test code organization
● DRY principle.● Readability. BDD vs. DRY● Consistency. Maintain the same style across
your codebase. ● Complexity. It may dictate the way you go.
Refactoring
Refactoring is about improving the design of existing code. It is the process of changing a software system in such a way that it does not alter the external behavior of the code, yet improves its internal structure.
Martin FowlerRefactoring: Improving the Design of Existing Code
Test behaviour not methods@Test public void testGetBalance() { assertEquals(0, account.getBalance())
}
@Test
public void shouldBeEmptyAfterCreation() { assertEquals(0, account.getBalance());
}
Test behaviour not methods
● Think of a contract ● And responsibilities● Specify requirements as tests
Test behaviour not methods
● Think of a contract ● And responsibilities● Specify requirements as tests● Happens naturally when done in test-first
approach
Matcher libraries
● Hamcrest - standard matcher lib for JUnit● AssertJ - fluent assertions (IDE friendly)
● Provide common matchers● You can write your own custom matchers
HamcrestassertThat(frodo.getName(), equalTo("Frodo"));
assertThat(frodo.getName(), is(equalTo("Frodo")));
assertThat(frodo.getName(), is("Frodo"));
//JUnit
assertEquals("Frodo", frodo.getName())
AssertJassertThat(frodo.getName()).isEqualTo("Frodo");
assertThat(frodo).isNotEqualTo(sauron).isIn(fellowshipOfTheRing);
assertThat(sauron).isNotIn(fellowshipOfTheRing);
//JUnit
assertEquals("Frodo", frodo.getName())
Custom matchers
● Help communicate test intention● Abstract assertion logic● Are reusable and save time in large projects● You may have a custom message to be
more specific about test failure
Custom matchers@Test
public void shouldHaveIsbnGenerated() {
Book book = new Book(1l, "5555", "A book");
assertThat(book, hasIsbn("1234"));}
fail()
In some cases (e.g. testing exceptions) you may want to force test to fail if some expected situation does not happen
fail()
try { // do stuff... fail("Exception not thrown");} catch(Exception e){ assertTrue(e.hasSomeFlag());}
fail()
● Fundamentally not bad, but better use matchers for expected failure
● Matchers help to clarify test intention● Don’t forget - expected behaviour is an
opposite of a failing test
Anti-pattern: The Ugly Mirror@Test
public void personToStringShouldIncludeNameAndSurname() {
Person person = new Person("Волк", "Серый");
String expected =
"Person[" + person.getName() + " " + person.getSurname() + "]"
assertEquals(expected, person.toString());
}
Anti-pattern: The Ugly Mirror@Test
public void personToStringShouldIncludeNameAndSurname() {
Person person = new Person("Волк", "Серый");
String expected =
"Person[" + person.getName() + " " + person.getSurname() + "]"
assertEquals(expected, person.toString());
}
Anti-pattern: The Ugly Mirror@Test
public void personToStringShouldIncludeNameAndSurname() {
Person person = new Person("Волк", "Серый");
assertEquals("Person[Волк Серый]", person.toString());
}
Ignoring tests
● Always use ignore/pending API from your test library (JUnit @Ignore)
@Ignore("charge simplicator not ready")
@Test public void shouldChargeMonthly() {
//implementation which fails
}
Ignoring tests
● Do not comment out or false assert your test//Will fix it later™
//@Test public void shouldBeZeroInitialy() {
// assertEquals(0, account.getBalance());
//}
@Test public void shouldBeZeroInitialy() {
assertEquals(1, account.getBalance());
}
Ignoring tests
● Do not comment out or false assert your test//Will fix it later™
//@Test public void shouldBeZeroInitialy() {
// assertEquals(0, account.getBalance());
//}
@Test public void shouldBeZeroInitialy() {
assertEquals(1, account.getBalance());
} Who is Will?
What to do with exceptions?
http://s273.photobucket.com/user/eliteskater08/media/meateatingrabbit.jpg.html
JUnit expected exception@Test(expected=IndexOutOfBoundsException.class)public void shouldThrowIndexOutOfBoundsException() { ArrayList emptyList = new ArrayList(); Object o = emptyList.get(0);}
//matcher in Specs2 (Scala)
server.process(None) must throwA[NothingToProccess]
try and catch
public void shouldThrowIndexOutOfBoundsException() { ArrayList emptyList = new ArrayList();
try { Object o = emptyList.get(0);
fail("Should throw IndexOutOfBoundsException");
} catch(IndexOutOfBoundsException e)){
//consider asserting message!
}}
catch-exception libList myList = new ArrayList();
catchException(myList).get(1);
assertThat(caughtException(),
allOf(
is(IndexOutOfBoundsException.class),
hasMessage("Index: 1, Size: 0"),
hasNoCause()
)
);
Exceptions
● What about ExpectedException Rule?○ My personal opinion - not that intuitive○ breaks arrange/act/assert flow
ExpectedException rule@Rule public ExpectedException exception = ExpectedException.none();
@Testpublic void testExpectedException() { exception.expect(IllegalArgumentException.class); exception.expectMessage(containsString('Invalid age')); new Person('Vilkas', -1);}
//Person constructor
public Person(String name, int age) { if (age <= 0) throw new IllegalArgumentException('Invalid age:' + age);
// ...
}
Testing with timehttp://wisconsinrelocation.net/post/1295775/tickle-your-funny-bone-----time-management-is-everything--
Problempublic class MyService { ...
public void process(LocalDate date) { if (date.isBefore(LocalDate.now()) { ... } else {
...
} }
}
Testing with Time
● Design your system where time is a collaborator
● Inject test specific time provider in your test○ constant time○ slow time○ boundary cases time
Control time with Clockpublic class MyService { private Clock clock; // dependency inject
...
public void process(LocalDate date) { if (date.isBefore(LocalDate.now(clock)) { ... } else {
...
} }
}
Collections● Most of the time you want to assert on collection content
assertThat(users, containsInAnyOrder("andrius", "vaidas"))
Collections● Avoid incomplete assertions
//users=List.of("andrius", "vaidas", "valdemaras", "jonas")
assertThat(users, hasItems("andrius", "vaidas"))
Collections● Do not sort just because it is easier to assert!
assertThat(sort(users), contains("andrius", "vaidas"))
Collections● Multiple assertions are worse than single content
assertion
assertThat(users, hasSize(2))
assertThat(users, hasItems("andrius", "vaidas"))
Random values in tests
● Most of the time you do not want it
@Test public void shouldStartWithFirst() {
String a = randomString();
String b = randomString();
assertThat(a + b, startsWith(a));
}
Random values in tests
● Unless you depend on randomness a lot (eg. password generation*)
*Thanks to Aleksandar Tomovski for a good example
Random values in tests
● Use property based testing (which is also hard)
//example from ScalaCheck
property("startsWith") = forAll { (a: String, b: String) =>
(a+b).startsWith(a)
}
Random values in tests
● Do not make dummy values randomcat = new Cat(randomString());
cat = new Cat("dummyName");
Generate Multiple Test Cases
● Quality over quantity● Think of boundary cases, that you may want
to detect with random test
Generate Multiple Test Cases
● Quality over quantity● Think of boundary cases, that you may want
to detect with random test● Use parameterized tests
Generate Multiple Test Cases
● Quality over quantity● Think of boundary cases, that you may want
to detect with random test● Use parameterized tests● Random is hard to repeat
Generate Multiple Test Cases
● Quality over quantity● Think of boundary cases, that you may want
to detect with random test● Use parameterized tests● Random is hard to repeat● Flickering tests
How many assertions per test?http://dailypicksandflicks.com/2012/05/11/daily-picdump-455/4-beers-at-the-same-time/
How many assertions per test?
● Unit test - one assertion per test. Must be clear and readable
● Proper tests should fail for exactly one reason
● End to end - best case one assertion per test, but more are allowed
● Consider custom matchers
How many assertions per test?
● Unit test - one assertion per test. Must be clear and readable
● Proper tests should fail for exactly one reason
● End to end - best case one assertion per test, but more are allowed
● Consider custom matchers
What can be better in this test? [pseudocode]
@Test shouldRetrieveUserByLogin() {
String userJson = "{\"username\": \"vaidas\"}";
HttpRequest post = new Post("https://localhost:8080/users", userJson);
HttpResponse postResp = HttpClient().execute(post);
assertThat(postResp.status, is(200));
HttpRequest get = new Get("https://localhost:8080/users/vaidas");
HttpResponse getResp = HttpClient().execute(get);
User user = mapper.readValue(getResp, User.class);
assertThat(user.username, is("vaidas"));
}
What can be better in this test? [pseudocode]
@Test shouldRetrieveUserByLogin() {
String userJson = "{\"username\": \"vaidas\"}";
HttpRequest post = new Post("https://localhost:8080/users", userJson);
HttpResponse postResp = HttpClient().execute(post);
assertThat(postResp.status, is( 200));
HttpRequest get = new Get("https://localhost:8080/users/vaidas");
HttpResponse getResp = HttpClient().execute(get);
User user = mapper.readValue(getResp, User.class);
assertThat(user.username, is("vaidas"));
}
Decoupling from low level details [pseudocode]
@Test shouldRetrieveUserByUsername() {
CreateUserResponse createResp = aCreateUserRequest().withUsername("vaidas").execute();
assertThat(createResp, isSuccessful());
GetUserResponse getResp = aGetUserRequest().withUsername("vaidas").execute();
assertThat(getResp, allOf(isSuccessful(), hasUsername("vaidas")));
}
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