Testing

The simplesource-command-testutils module includes utility classes to help test your implementation.

AggregateTestDriver implements the CommandAPI interface. It uses the Kafka Streams TopologyTestDriver test tool to run the same topology used by the Simple Sourcing production code in your tests, mocking out Kafka, the Schema Registry and the communication between the command API and the Simple Sourcing instances.

AggregateTestHelper provides a DSL built on top of AggregateTestDriver for chaining together publication of commands and making assertions about the inner state of the event sourcing library after each command. It also provides a simple mechanism to validate the correct event and aggregate state changes occur as a result of each command.

An example is given below. We insert a new user then update their name. In each case we provide the expected events and projection state.

The second command will automatically get sent with the same key and sequence number of the last event from the previous command.

testHelper.publishCommand(
    id,
    Sequence.first(),
    new UserCommand(new InsertUser(firstName, lastName)))
    .expecting(
        NonEmptyList.of(new UserEvent(new UserInserted(firstName, lastName))),
        Optional.of(new User(id, firstName, lastName, null))
    )
    .thenPublish(
        new UserCommand(new UpdateName(updatedFirstName, updatedLastName)))
    .expecting(
        NonEmptyList.of(
            new UserEvent(new FirstNameUpdated(updatedFirstName)),
            new UserEvent(new LastNameUpdated(updatedLastName))),
        Optional.of(new User(id, updatedFirstName, updatedLastName, null))
    )

There is also a variation of the thenPublish method where you provide a function that takes the last projection value and sequence and produces a new command with your own provided sequence id. This is useful when you’re testing error scenarios. Below we’re creating a new user then we’re sending an update command with an invalid sequence id. We indicate we expect an error providing the expected failure reason.

testHelper.publishCommand(
    id,
    Sequence.first(),
    new UserCommand(new InsertUser(firstName, lastName)))
    .expecting(
        NonEmptyList.of(new UserEvent(new UserInserted(firstName, lastName))),
        Optional.of(new User(id, firstName, lastName, null))
    )
    .thenPublish(update ->
        new ValueWithSequence<>(new UserCommand(new UpdateName(updatedFirstName, updatedLastName)), Sequence.first()))
    .expectingFailure(NonEmptyList.of(InvalidReadSequence))