JUnit is the standard way to test things in Java. In fact, it is the most commonly included external library for Java projects! Here is another fact - JUnit 4 release was 11 years ago and no feature releases were added in recent years. What you knew about JUnit in 2010 is still 100% relevant today. In 2017... So finally, time for an upgrade! What took 11 years? What is new? What changed and what stayed the same? What about IDE and build tool support? What will testing on the JVM look like in the future? Check the presentation and you will find out.

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JUnit 5
Kostadin Golev
CTO @ Rewards Labs
The Next Generation

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Why JUnit 5?
Where Is It?
Writing Tests
Platform For The JVM
Running Along JUnit 3 & 4
Important New Features
IDE & Tool Support

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Issues with JUnit 4

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How bad?
Let’s rename some private variables to find out!

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4.11:
org.junit.ComparisonFailure:
expected:<[1]L> but was:<[2]L>
assertEquals(1, 2)

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4.12-beta-1:
org.junit.ComparisonFailure:
expected: null<null> but was: null<null>
assertEquals(1, 2)

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Extension mechanism
Runner
@RunWith(SpringJUnit4ClassRunner.class)
Rule
@Rule ExpectedException thrown = none()

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Powerful Composable
Runner Rule

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Extension mechanism
Powerful Composable?
Runner Rule

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Why JUnit 5?
Where Is It?
Writing Tests
Platform For The JVM
Running Along JUnit 3 & 4
Important New Features
IDE & Tool Support

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Will this work?

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There is no single JUnit 5
(JAR)

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Not one big fat jar
We have more then ten now, in three groups

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JUnit Platform
+
JUnit Jupiter
+
JUnit Vintage
JUnit 5

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JUnit Platform

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JUnit Jupiter
JUnit Vintage

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Why JUnit 5?
Where Is It?
Writing Tests
Platform For The JVM
Running Along JUnit 3 & 4
Important New Features
IDE & Tool Support

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@Test
void exception() {
RuntimeException thrown =
assertThrows(RuntimeException.class, () ->
library.throwRuntimeException("message")
);
assertEquals("message", thrown.getMessage());
}

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What about Runners and
Rules?

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We wrote some tests!
How do we run them?

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Why JUnit 5?
Where Is It?
Writing Tests
Platform For The JVM
Running Along JUnit 3 & 4
Important New Features
IDE & Tool Support

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Some History
Or how JUnit 5 team discovered they were building a
platform

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It started as a big fat jar
Then everything got split in small, focused modules

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Launcher
<<interface>>
Engine
Engine Impl
Jupiter API
implements
JUnit Platform
JUnit Jupiter

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Launcher
<<interface>>
Engine
JUnit Platform

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<<interface>>
Engine
Engine Implementation
implements
JUnit Platform
JUnit Jupiter

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Jupiter API
JUnit Jupiter
@Test
@BeforeEach
assertEquals()
…

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testRuntime “org.junit.jupiter:junit-jupiter-engine:5.0.0”
<plugin>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.19.1</version>
<dependencies>
…
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-engine</artifactId>
<version>5.0.0</version>
</dependency>
</dependencies>
</plugin>

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Why JUnit 5?
Where Is It?
Writing Tests
Platform For The JVM
Running Along JUnit 3&4
Important New Features
IDE & Tool Support

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You can still run your
JUnit 3&4 tests
But it will not be JUnit 3&4 running them

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Launcher
<<interface>>
Engine
Vintage Engine Impl
JUnit 3&4 API
implements
JUnit Platform
JUnit Vintage

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JUnit Platform
JUnit Jupiter JUnit Vintage
JUnit5 tests JUnit4 tests

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testRuntime “org.junit.jupiter:junit-jupiter-engine:5.0.0”
testRuntime “org.junit.vintage:junit-vintage-engine:5.0.0”

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Platform for the JVM
Many Developers implemented their own engines,
reusing JUnit5 tool integration

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Not only for Java
Test Engine implementations exist for
Scala, Kotlin and Groovy

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Why JUnit 5?
Where Is It?
Writing Tests
Platform For The JVM
Running Along JUnit 3 & 4
Important New Features
IDE & Tool Support

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assertAll(…)

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assertEquals(1, 2);
assertEquals("String", "Another String");
org.opentest4j.AssertionFailedError:
Expected :1
Actual :2

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assertAll(
() -> assertEquals(1, 2),
() -> assertEquals("String", “Another String")
)
org.opentest4j.MultipleFailuresError: Multiple Failures (2 failures)
expected: <1> but was: <2>
expected: <String> but was: <Another String>

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What about Runners and
Rules (again)?
JUnit5 Extension model

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@ExtendWith

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Composable & Powerful
Use as many as you want
whenever you want them

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@ExtendWith(SpringExtension.class)
@ExtendWith(MockitoExtension.class)
class SpringTest {
@Autowired
SpringComponent component;
@Mock
Dependency mocked;

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class ParameterInTestMethods {
@Test
@ExtendWith(MockitoExtension.class)
void test(@Mock Dependency mocked) {
…
}

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public class MockitoExtension implements
TestInstancePostProcessor {
@Override
public void postProcessTestInstance(
Object testInstance,
ExtensionContext context) {
MockitoAnnotations.initMocks(testInstance);
}
}

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Some official extensions
SpringExtension - since Spring 5.0 (Sep 2017)
MockitoExtension - since 2.17.0 (Mar 2018)

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@Nested
@DisplayName

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public class Library {
private Books books;
public Library(Books books) {
this.books = books;
}
public void addBook(Book book) {
// do something with books
}
}

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@Test
void whenBookExistsThenIncrementAmount() {}
@Test
void whenBookExistsThenCheckAmountMoreThenN() {}
@Test
void whenBookDoesNotExistThenCreateBook() {}
@Test
void whenBookDoesNotExistThenSendNewBookNotification() {}

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Tests are often a tree,
not a list

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@DisplayName("Book is added to library")
class BookAddedTest {
@DisplayName("when book exists")
@Nested
class whenBookExists {
@DisplayName("amount++")
@Test
void incrementAmount() {}
@DisplayName("check amount > limit")
@Test
void checkAmountMoreThenLimit() {}
}
. . .
}

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@ParameterizedTest

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testCompile “org.junit.jupiter:junit-jupiter-params:5.0.0"
<dependency>
<groupId>org.junit.jupiter</groupId>
<artifactId>junit-jupiter-params</artifactId>
<version>5.0.0</version>
<scope>test</scope>
</dependency>
WARNING!
WARNING!
WARNING!

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@Test
void strIsLessThenTenChar() {
int value = "str".length();
assertTrue(value < 10);
}
@Test
void StringIsLessThenTenChar() {
int value = "String".length();
assertTrue(value < 10);
}

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@ValueSource(strings = {“str”, “String”})
@ValueSource(ints = {1, 3, 7, 9})
@EnumSource(SomeEnum.class)
@CsvSource({"1, 1", "2, 4", "4, 16”})
@CsvFileSource(resources=“testData.csv”)

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@MethodSource(names=“stringAndIntProvider")
…
static Stream<Arguments> stringAndIntProvider() {
return Stream.of(
ObjectArrayArguments.create("foo", 3),
ObjectArrayArguments.create("foobar", 6)
);
}

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enum Status {
OK, INVALID_NAME, INVALID_DATE, …
}
@ParameterizedTest
@EnumSource(value = Status.class, mode = EXCLUDE,
names = “OK")
void should_return_error_when_not_OK(Status status) {
…

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Why JUnit 5?
Where Is It?
Writing Tests
Platform For The JVM
Running Along JUnit 3 & 4
Important New Features
IDE & Tool Support

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Also supported pre-GA releases
Since Oxygen 4.7.1

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Surefire provider
Not native yet
Native support since 4.6
Plugin

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testCompile "org.junit.jupiter:junit-jupiter-api:5.0.0"
testRuntime "org.junit.jupiter:junit-jupiter-engine:5.0.0"
testCompile "org.junit.jupiter:junit-jupiter-params:5.0.0"
…
test {
useJUnitPlatform {
includeEngines 'junit-jupiter', 'junit-vintage'
}
failFast = true
}

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junit.org/junit5

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Questions?
@kotseto
kgolev.com/talks/junit5