Testing with JUnit5

What in new in JUnit Jupiter

Visibility
- Everything does not have to be public
Custom display names
- @DisplayName: spaces, special characters, emoji 👻
- DisplayNameGenerator
Tagging
- @Tag
- Tag expression language
Meta-annotation support
- Create your own custom composed annotations
- Combine annotations from Spring and JUnit
Conditional test execution
Dependency injection for constructors and methods
Lambda expressions and method references
Interface default methods and testing traits
@Nested test classes
@RepeatedTest, @ParameterizedTest, @TestFactory
@TestInstance lifecycle management
Implicit / Explicit conversions
Argument aggregation
New extension model
- Extension: marker interface
- APIs: org.junit.jupiter.api.extension
- @ExtendWith(...)
- @RegisterExtension
And more ...

Architecture

Dependencies

2 + 1 or more dependencies (depending on if you want legacy and/or 3d party engines):

<dependency>
    <groupId>org.junit.jupiter</groupId>
    <artifactId>junit-jupiter-engine</artifactId>
    <version>${junit.jupiter.version}</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.junit.jupiter</groupId>
    <artifactId>junit-jupiter-api</artifactId>
    <version>${junit.jupiter.version}</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.junit.vintage</groupId>
    <artifactId>junit-vintage-engine</artifactId>
    <version>5.4.2</version>
    <scope>test</scope>
</dependency>

Testing

Making Existing Code Testable

Common issues:

Mixed concerns
Problematic dependencies

Mixed concerns

They violate the single responsibility principle. This can make it hard to:

Access system output to apply assertions (for example outputting them to a file or report)
Provide inputs to the code under test (when ui code is mixed with business code)
Avoid undesired side effects (for example db access, either unavailability or slow)

Solution:

Extract and separate the code to test.

Problematic dependencies

They can make testing difficult due to:

Side effects
Talking to remote services that aren't always present
Inconsistent behavior

Solution:

Provide a test double for the dependency (through DI), without the harmful side effects or external dependencies. Libraries like Mockito or EasyMock make this very easy and prevent the clutter of extra classes / files.

H3AR7B3A7 / JUnit5