Domain Modeling

Distill

Requirements are expressed as scenarios.

A scenario represents the system's behavior from the user's perspective and follows the Given-When-Then structure to create a testable specification.

The specification is written as executable tests, which are automated and run continuously. These tests cover a full range of scenarios, from happy paths to error cases.

Success Scenario(s)

Focus on a single command!

For the ChangeMenu command to succeed, you need to specify the required preconditions/events. In this case RestaurantCreated / Exists is a precondition.

RestaurantCreated / Exists might not be the only precondition. For example, "The menu must be in a modifiable state (e.g., not locked due to an active promotion or regulations)"

lib/domain_test.ts

Deno.test(function changeRestaurantMenuDeciderTest() {
  const changeRestaurantMenuCommand: RestaurantCommand = restaurantCommandSchema
    .parse(
      JSON.parse(changeRestaurantMenuCommandJson),
    );

  const restaurantCreatedEvent: RestaurantEvent = restaurantEventSchema
    .parse(
      JSON.parse(restaurantCreatedEventJson),
    );

  const restaurantMenuChangedEvent: RestaurantEvent = restaurantEventSchema
    .parse(
      JSON.parse(restaurantMenuChangedEventJson),
    );

  DeciderSpecification.for(restaurantDecider)
    .given([restaurantCreatedEvent])
    .when(changeRestaurantMenuCommand)
    .then([restaurantMenuChangedEvent]);
});

Error Scenario(s)

Focus on a single command!

Define all the possible reasons why ChangeMenu command can fail. In this case RestaurantCreated / Exists is missing as a precondition.

RestaurantCreated / Exists might not be the only missing precondition. For example, "The menu must be in a modifiable state (e.g., not locked due to an active promotion or regulations)"

lib/domain_test.ts

Deno.test(function changeRestaurantMenuDeciderTest() {
  const changeRestaurantMenuCommand: RestaurantCommand = restaurantCommandSchema
    .parse(
      JSON.parse(changeRestaurantMenuCommandJson),
    );

  const restaurantMenuNotChangedEvent: RestaurantEvent = restaurantEventSchema
    .parse(
      JSON.parse(restaurantMenuNotChangedEventJson),
    );

  DeciderSpecification.for(restaurantDecider)
    .given([])
    .when(changeRestaurantMenuCommand)
    .then([restaurantMenuNotChangedEvent]);
});