Developer Tests - Things to Know (Vilnius JUG)

Developer Tests
Things to Know
Vaidas Pilkauskas 2014
Vilnius JUG
vaidas.pilkauskas@gmail.com

me
My 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 me
connect 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 Rennella
http://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

Developer Tests - Things to Know (Vilnius JUG)

“Legacy Code is code without
Tests”
Michael Feathers
Working Effectively with Legacy Code

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

Test phases
Setup
Exercise
Verify
Teardown

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
}

Refactor to lifecycle methods
@Before public void before() {
server = new NotesServer(); // setup
note = new Note("test note"); // setup
}
@Test public void serverShouldAddNoteSuccessfully() {
}
@After public void after() {
}

DON’Ts - #1
Do not start from setup/teardown

DON’Ts - #2
Do not mix setup code from different
tests - shared code must be relevant to
the tests that use it

DON’Ts - #3
Setup and teardown are there to solve
DRY problem and to help structure your
test code

How many colors are there in the
picture?
Source: Josef Albers Interaction of Color

Context matters!
Source: Josef Albers Interaction of Color

Typical setup inside @Before
}
}
@After public void after() { server.shutdown(); // teardown }

Setup pollution - #1
● Every line in setup must be relevant to all tests.

● It is tempting to add additional setup tuning just to
fix/enhance one test.

● Rich setup makes tests slow!

● Setup is to bootstrap your SUT.

● Setup hides details! Do not hide test preconditions.

Setting up “job” inside test method
}
}

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
}

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 Fowler
Refactoring: Improving the Design of Existing Code

Test behaviour not methods
● Think of a contract

● And responsibilities

● Specify requirements as tests

● Specify requirements as tests
● Happens naturally when done in test-first
approach

Matchers
● Enhance readability
● Asserts 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)
● Provides common matchers
● You can write your own custom matchers

Hamcrest
assertThat(frodo.getName(), equalTo("Frodo"));
assertThat(frodo.getName(), is(equalTo("Frodo")));
assertThat(frodo.getName(), is("Frodo"));

AssertJ
assertThat(frodo.getName()).isEqualTo("Frodo");
assertThat(frodo).isNotEqualTo(sauron).isIn(fellowshipOfTheRing);
assertThat(sauron).isNotIn(fellowshipOfTheRing);

Custom matchers
Are matchers that we write 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 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

Thing #6
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());
}

@Test
public void personToStringShouldIncludeNameAndSurname() {
Person person = new Person("Vilkas", "Pilkas");
assertEquals("Person[Vilkas Pilkas]", person.toString());
}

Thing #7
How to turn off the test?

Why would you want 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
● Do not comment out or false assert your test

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

Thing #8
What to do with exceptions?

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

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!
}
}

Exceptions
● catch-exception lib

catch-exception lib
List 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();
@Test
public 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);
// ...
}

Problem
public 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 Clock
public class MyService {
private Clock clock; // dependency inject
...
public void process(LocalDate date) {
if (date.isBefore(LocalDate.now(clock)) {
...
}
}
}

Collections - multiple properties to
assert
● Is null?
● Size
● Order
● Content

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

Collections
● Prefer exact content matching

Collections
● Avoid incomplete assertions

Collections
● Do not sort just because it is easier to assert!

Collections
● Multiple assertions are worse than single content
assertion

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

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

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

● Unless you depend on randomness a lot
● Use property based testing (which is also
hard)

● 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

● Think of boundary cases, that you may want
to detect with random test

● Use parameterized tests

● Random is hard to repeat

● Random is hard to repeat
● Flickering tests

Thing #12
How many assertions per test?

● Unit test - one assertion per test. Must be
clear and readable
● Proper test should fail for exactly one reason
● End to end - best case one assertion per
test, but more are allowed
● Consider custom matchers

● Unit test - one assertion per test. Must be
clear and readable
● Proper test should fail for exactly one
reason
● End to end - best case one assertion per
test, but more are allowed
● Consider custom matchers

Thing #13
Decoupling in End-to-end tests

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(username, is("vaidas"));
}

Decoupling from low level details
[pseudocode]
@Test shouldRetrieveUserByUsername() {
CreateUserResponse createResp = aCreateUserRequest().withUsername("vaidas").execute();
assertThat(createResp, hasStatus(OK));
GetUserResponse getResp = aGetUserRequest().withUsername("vaidas").execute();
assertThat(getResp, allOf(hasStatus(OK), hasUsername("vaidas")));
}

Thoughts on end-to-end testing
● What is real e2e? REST vs. UI
● Testing by using system itself
● Vs. using low level DB driver to verify data
persistence

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 methods

Summary
● Context matters
● Tests are controversial topic
● And very opinionated

Developer Tests - Things to Know (Vilnius JUG)

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