Developer TestsThings to Know

Vaidas Pilkauskas 2014 Kaunas JUG

vaidas.pilkauskas@gmail.com

“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 I’m going to talk 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

“Legacy Code is code without Tests”

Michael FeathersWorking Effectively with Legacy Code

So what is test?

It is system’s exercise under predefined conditions and then verification of an expected outcome.

Thing #1Test phases

Test phases

1. Set up2. Exercise 3. Verify4. Tear down

Test phases@Test public void serverShouldExecuteJobSuccessfully() {

Server server = new Server(); // set up

Job job = new Job(); // set up

Status status = server.execute(job); // exercise

assertEquals(SUCCESS, status); // verify

server.shutdown(); // tear down

}

@Before public void before() {

server = new Server();

}

@Test public void serverShouldExecuteJobSuccessfully() {

Job job = new Job(); // set up

Status status = server.execute(job); // exercise

assertEquals(SUCCESS, status); // verify

server.shutdown(); // tear down

}

@Before public void before() {

server = new Server();

Job job = new Job();

}

@Test public void serverShouldExecuteJobSuccessfully() {

Status status = server.execute(job); // exercise

assertEquals(SUCCESS, status); // verify

server.shutdown(); // tear down

}

@Test public void serverShouldQueueJobWithFutureDate() {

// * set up which is actual for the current method

// * use scope specific name

Job futureJob = new Job(futureDate()); // set up

Status status = server.execute(futureJob); // exercise

assertEquals(SUCCESS, status); // verify

server.shutdown(); // tear down

}

@Before public void before() {

server = new Server();

Job job = new Job();

}

@Test public void serverShouldExecuteJobSuccessfully() {

Status status = server.execute(job); // exercise

assertEquals(SUCCESS, status); // verify

}

@After public void after() {

server.shutdown(); // tear down

}

@Before ..

@Test public void serverShouldExecuteJobSuccessfully() {

// * no need to name intermediate var, but

// * may hide return meaning of server.execute()

// execute & verify

assertEquals(SUCCESS, server.execute(job));

}

@After ..

Set up

● DRY principle

Set up

● DRY principle● Readability

Set up

● DRY principle● Readability● Consistency

Set up

● DRY principle● Readability● Consistency● Complexity

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

Thing #2What do we test?

Test behaviour not methods

● Think of a contract

Test behaviour not methods

● Think of a contract ● And responsibilities

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

Thing #3Matchers

Matchers

● Enhanced readability● Assertions on the right level of abstraction● Encapsulate testing logic● Reusable● Detailed match error messages (do not

leave them out in your custom matchers!)

Matcher libraries

● Hamcrest - standard matcher lib for JUnit● AssertJ - fluent assertions (IDE friendly)

● Bring common matchers for you to use● Write your own custom matchers

HamcrestassertThat(theBiscuit, equalTo(myBiscuit));

assertThat(theBiscuit, is(equalTo(myBiscuit)));

assertThat(theBiscuit, is(myBiscuit));

AssertJassertThat(frodo.getName()).isEqualTo("Frodo");

assertThat(frodo).isNotEqualTo(sauron) .isIn(fellowshipOfTheRing);

assertThat(sauron).isNotIn(fellowshipOfTheRing);

Thing #4Custom matchers

Custom matchers

Are matchers we develop specifically for our projects

Custom matchers

● Help communicate test intention● Abstract assertion logic in case standard

matchers are not enough● Are reusable and save time in large projects● You may have custom message to be more

specific about test failure

Custom matchers@Test

public void testBookIsbn() {

Book book = new Book(1l, "5555", "A book");

assertThat(book, hasIsbn("1234"));}

Thing #5Failing test

fail()

In some cases like 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

Thing #6Anti-pattern: The Ugly Mirror

Anti-pattern: The Ugly Mirror@Test

public void personToStringShouldIncludeNameAndSurname() {

Person person = new Person("Vilkas", "Pilkas");

String expected =

"Person[" + person.getName() + " " + person.getSurname() + "]"

assertEquals(expected, person.toString());

}

Anti-pattern: The Ugly Mirror@Test

public void personToStringShouldIncludeNameAndSurname() {

Person person = new Person("Vilkas", "Pilkas");

String expected =

"Person[" + person.getName() + " " + person.getSurname() + "]"

assertEquals(expected, person.toString());

}

Anti-pattern: The Ugly Mirror@Test

public void personToStringShouldIncludeNameAndSurname() {

Person person = new Person("Vilkas", "Pilkas");

assertEquals("Person[Vilkas Pilkas]", person.toString());

}

Thing #7How to turn off the test?

Why would you want to turn off the test?

● Well, because it fails… :)

Ignoring tests

● Always use ignore/pending API from your test library (JUnit @Ignore)

Ignoring tests

● Always use ignore/pending API from your test library (JUnit @Ignore)

● Do not comment out or false assert your test

Ignoring tests

● Always use ignore/pending API from your test library (JUnit @Ignore)

● Do not comment out or false assert your test● If you do not need a test - delete it

Thing #8What to do with exceptions?

Exceptions

● If you can, use matchers instead of○ @Test(expected=?)

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]

Exceptions

● If you can, use matchers instead of○ @Test(expected=?)○ try-catch approach

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!

}}

Exceptions

● If you can, use matchers instead of○ @Test(expected=?)○ try-catch approach

● catch-exception lib

catch-exception libList myList = new ArrayList();

catchException(myList).get(1);

assertThat(caughtException(),

allOf(

is(IndexOutOfBoundsException.class),

hasMessage("Index: 1, Size: 0"),

hasNoCause()

)

);

Exceptions

● If you can, use matchers instead of○ @Test(expected=?)○ try-catch approach

● catch-exception lib● 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);

// ...

}

Thing #9How to test asynchronous code?

Asynchronous code

● Do not Thread.sleep - makes test slow

Asynchronous code

● Do not Thread.sleep - makes test slow● Use Awaitility, or similar DSL for

synchronizing asynchronous operations

Awaitility (Java 8 example)@Testpublic void shouldPersistNewUser() { publish(new CreateUserCommand("Vilkas Pilkas"));

await().until(userRepo::size, is(1));

//how long to await? (Default is 10 seconds) await().until(userRepo::isNotEmpty);}

Asynchronous code

● Do not Thread.sleep - makes test slow● Use Awaitility, or similar DSL for

synchronizing asynchronous operations● Use reasonable await time to avoid flaky

tests

Thing #10Testing with time

Problempublic class MyService {

...

public void process(LocalDate date) { if (date.isBefore(LocalDate.now()) { ... } }

}

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)) { ... } }

}

Thing #11Collections

Collections - multiple properties to assert

● Is null?● Size● Order● Content

Collections● Most of the time you want to assert on collection content

Collections● Most of the time you want to assert on collection content● Prefer exact content matching

Collections● Most of the time you want to assert on collection content● Prefer exact content matching● Avoid incomplete assertions

Collections● Most of the time you want to assert on collection content● Prefer exact content matching● Avoid incomplete assertions● Do not sort just because it is easier to assert!

Collections● Most of the time you want to assert on collection content● Prefer exact content matching● Avoid incomplete assertions● Do not sort just because it is easier to assert!● Multiple assertions are worse than single content

assertion

Collections● Most of the time you want to assert on collection content● Prefer exact content matching● Avoid incomplete assertions● Do not sort just because it is easier to assert!● Multiple assertions are worse than single content

assertion● Unless you want to say something important in your test!

Collections● Most of the time you want to assert on collection content● Prefer exact content matching● Avoid incomplete assertions● Do not sort just because it is easier to assert!● Multiple assertions are worse than single content

assertion● Unless you want to say something important in your test!● Use matchers!

Thing #12Access modifiers

Access modifiers

● Rule is simple - never access anything that is not public in your tests

Access modifiers

● Rule is simple - never access anything that is not public in your tests

● Private things are implementation details which are not part of the public contract

Access modifiers

● Rule is simple - never access anything that is not public in your tests

● Private things are implementation details which are not part of the public contract

● Same applies for protected/package modifiers. They must be there for production code, but not available to your tests

Thing #13Random values

Random values in tests

● Most of the time you do not want it

Random values in tests

● Most of the time you do not want it● Unless you depend on randomness a lot (eg.

password generation*)

*Thanks to Aleksandar Tomovski for a good example

Random values in tests

● Most of the time you do not want it● Unless you depend on randomness a lot● Use property based testing (which is also

hard)

Random values in tests

● Most of the time you do not want it● Unless you depend on randomness a lot● Use property based testing (which is also

hard)● Do not make dummy values random

What if we still need random cases?

Generate Multiple Test Cases

● Quality over quantity

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

Thing #14How many assertions per test?

How many assertions per test?

● Unit test - one assertion per test. Must be clear and readable

● Proper unit tests should fail for exactly one reason

● End to end - best case one assertions per test, but more allowed

● Consider custom matchers

Thing #15Test Doubles

Test Doubles

The name comes from the notion of a Stunt Double in movies

Why do we need test doubles?

● To test in an isolated environment by replacing real collaborators with doubles

● To have fast tests● To test interactions● To change collaborators behaviour in test

Types of Test Doubles

● Dummy● Fake● Stub● Spy● Mock

Dummy

Dummy objects are passed around but never actually used. Usually they are just used to fill parameter lists

Fake

Fake objects actually have working implementations, but usually take some shortcut which makes them not suitable for production (an in memory database is a good example)

Stub

Stubs provide canned answers to calls made during the test, usually not responding at all to anything outside what's programmed in for the test. Stubs may also record information about calls, such as an email gateway stub that remembers the messages it 'sent', or maybe only how many messages it 'sent'

Spy

Stubs that verify behavior

Mock

Mocks are what we are talking about here: objects pre-programmed with expectations which form a specification of the calls they are expected to receive

So what’s the difference between Spy and Mock?

Thing #16Naming

Where to keep your tests

● Recommendation: keep them in separate package from production code

Class Naming

● End test classes with Test suffix (or one required by your test framework)

● For long test classes:○ split by feature○ by input type

Method Naming

● Everybody should follow the same pattern● testGeneratePassword vs

shouldGenerateValidPassword

Naming Test Doubles

● Intention revealing stubEngine, spyServer, dummyUser, mockService

Thing #17Comments

Comments in Test code

● Fundamentally good option to explain complicated parts, but:

● better use good method naming● custom matcher● do less, so that intention is clear● comments are not so bad in isolated well

named set up method (not the first thing to be seen in test method)

Thanks!Q & A