Execute tests concurrently using Project Reactor

How to write tests using reactive programming

A publisher represents a sequence of events. Each event may be processed by operators, and the sequence may terminate with a completion or an error.

By representing test cases as publishers, we can more simply reason about concurrency and parallelism, and leverage efficiency gains from non-blocking high-latency processing (usually associated with testing remote services).

Test cases are represented as Mono<Serializable>. The emission of the mono should represent a serializable test result. This choice does not detract from the expressiveness of reactive streams, because internally, a test method may choose to use a longer Flux, then process the events in order to determine a pass/fail test result and associated result data.

Try running the example in project-reactor-test-execution-examples!

Set up on local

Make a ~/.m2/repository directory, then run

./gradlew publishToMavenLocal

May require a maven install, not sure.

How to configure the "reactor" test engine for junit platform

1. Add the dependency on project-reactor-junit-platform-engine. You will also need reactor core for Flux/Mono.

testImplementation 'com.segbaus:project-reactor-junit-platform-engine:${reactor-test-engine-version}'
implementation platform('io.projectreactor:reactor-bom:${reactor-bom-version}')
implementation 'io.projectreactor:reactor-core'

2. Mark your test classes with JUnit's @IncludeEngines

@IncludeEngine("reactor")
public class MyTestClass() {
  ...
}

3. Mark your static test methods with @ReactorTest

@ReactorTest
public static Mono<MyTestResultType> myTestMethod() {
    ...
}

Notes:

• You must declare all test methods static. The test engine will not instantiate the test classes.
• The test case will fail iff the Mono terminates with an error.

How to create reusable test components

Just write classes/methods that return CorePublishers, and then compose them as you wish! ez

To do list

1. Add a way to represent a partial ordering of test methods.
2. Add utilities for testing remote services using reactive web client (esp. ui).
3. Add option to represent test cases using gherkin feature files and step definitions.
4. Add an integration with JQuik for properties-based testing and test data generation.
5. Add test parameters.

References

1. Project reactor: https://github.com/reactor
2. Junit5: https://junit.org/junit5/