projection-test-builder

name	projection-test-builder
description	Generate projection integration tests from STATE_VIEW specifications

Projection Test Builder Skill

Overview

Generate projection integration tests from STATE_VIEW slice specifications. Tests verify read model projection behavior using given/then structure.

When to Use

• STATE_VIEW slice with specifications defined
• Specifications contain given (events) and then (expected read model state)

Input Structure

{
  "specifications": [
    {
      "title": "spec: cart items with removed item",
      "given": [
        { "title": "Cart Created", "type": "SPEC_EVENT", "fields": [...] },
        { "title": "Item Added", "type": "SPEC_EVENT", "fields": [...] }
      ],
      "then": [
        { "title": "cart items", "type": "SPEC_READMODEL", "fields": [...] }
      ],
      "comments": [{ "description": "Read Model should display an empty list" }]
    }
  ]
}

Generation Steps

Step 1: Determine Test Location

Location: src/test/java/de/eventmodelers/<context>/slices/<slicename>/<SliceName>ProjectionTest.java

Step 2: Convert Event Names

• "Item Added" → ItemAddedEvent
• "Cart Created" → CartCreatedEvent

Step 3: Generate Test Class

package de.eventmodelers.<context>.slices.<slicename>;

import de.eventmodelers.<context>.slices.<slicename>.<SliceName>ReadModel;
import de.eventmodelers.<context>.slices.<slicename>.<SliceName>ReadModelQuery;
import de.eventmodelers.common.support.BaseIntegrationTest;
import de.eventmodelers.common.support.ProjectionFixtureConfiguration;
import de.eventmodelers.common.support.RandomData;
import de.eventmodelers.domain.<Aggregate>Aggregate;
import de.eventmodelers.events.*;
import org.axonframework.modelling.command.Repository;
import org.axonframework.queryhandling.QueryGateway;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;

import java.util.UUID;

import static de.eventmodelers.common.support.TestUtils.awaitUntilAsserted;
import static org.assertj.core.api.Assertions.assertThat;

class <SliceName>ProjectionTest extends BaseIntegrationTest {
    @Autowired
    private QueryGateway queryGateway;

    @Autowired
    private Repository<<Aggregate>Aggregate> repository;
}

Step 4: Generate Test Methods

@Test
void <specTitleAsCamelCase>() {
    var aggregateId = UUID.randomUUID();

    var fixture = ProjectionFixtureConfiguration.aggregateInstance(
        () -> repository.newInstance(<Aggregate>Aggregate::new)
    );

    // Apply events from given[]
    fixture.given(
        RandomData.newInstance(<EventName>Event.class, event -> {
            event.setAggregateId(aggregateId);
        })
    );
    fixture.apply();

    // Verify read model state from then[]
    awaitUntilAsserted(() -> {
        var readModel = queryGateway.query(
            new <SliceName>ReadModelQuery(aggregateId),
            <SliceName>ReadModel.class
        ).join();

        assertThat(readModel).isNotNull();
        // Assert expected field values from then[]
    });
}

Field Handling

• UUID with idAttribute: true - Use shared UUID across related events
• Example values - Use for assertions: "example": "9.99" → assertThat(price).isEqualTo(9.99)
• Mapping attribute - "mapping": "productId" means map from productId field

Assertion Patterns

Scenario	Assertion
Empty list	assertThat(readModel.data()).isEmpty()
List size	assertThat(readModel.data()).hasSize(2)
Field value	assertThat(readModel.data().totalPrice()).isEqualTo(19.98)
Existence	assertThat(readModel).isNotNull()