comparison-example

Comparison Example — With Skill vs. Without Skill

A single feature (Order Management: create order, apply a threshold discount, fetch by ID, search by customer) implemented twice:

• without-skill/ — how an agent commonly writes it with no guidance: one God-class controller, JPA entities exposed directly as the API model, field injection, double for money, a string-concatenated JPQL query (injection risk), swallowed exceptions, zero tests.
• with-skill/ — the same feature with the senior-engineer skill applied: layered (controller → service → domain → repository), DTOs at the boundary, a Money value object, constructor injection, a Strategy pattern for the discount rule (Open/Closed), domain exceptions + @RestControllerAdvice, parameterized queries, and JUnit/Mockito tests.

See the root README.md's "Comparison Example" section for a full side-by-side write-up of every difference and why it matters.

Verifying it compiles

Neither project can reach Maven Central from a locked-down sandbox, so _stub-spring-api/ is a minimal hand-written stub of the Spring Boot/JPA/JUnit/Mockito surface both projects actually use — enough to type-check real code, not a mock framework.

./verify-compile.sh

This compiles both projects against the stub and actually executes OrderPolicyTest (pure JUnit, no mocking needed) to confirm the discount math is genuinely correct — not just that the code parses. OrderServiceTest/OrderControllerTest use Mockito, which the stub doesn't functionally implement (no bytecode-level mocking), so those are verified to compile/type-check correctly; run them for real with mvn test once you have internet access to Maven Central.

Running for real

Both are normal Spring Boot Maven projects:

cd with-skill    # or without-skill
mvn spring-boot:run