Add tests for RelationProcessor

testing/pom.xml

@@ -43,6 +43,10 @@
             <groupId>org.flywaydb</groupId>
             <artifactId>flyway-database-postgresql</artifactId>
         </dependency>
+        <dependency>
+            <groupId>com.google.testing.compile</groupId>
+            <artifactId>compile-testing</artifactId>
+        </dependency>
     </dependencies>
 
     <build>

testing/src/main/java/at/test/drm/DogEntity.java

@@ -2,19 +2,16 @@
 
 import at.drm.annotation.Relation;
 import at.drm.model.RelationIdentity;
+import jakarta.persistence.*;
 import lombok.Data;
 
-import jakarta.persistence.Entity;
-import jakarta.persistence.GeneratedValue;
-import jakarta.persistence.GenerationType;
-import jakarta.persistence.Id;
-
 @Relation
 @Entity
 @Data
 public class DogEntity implements RelationIdentity {
 
     @Id
     @GeneratedValue(strategy = GenerationType.IDENTITY)
+    @Column(unique = true, nullable = false)
     private Long id;
 }

testing/src/test/java/at/test/drm/RelationProcessorTest.java

@@ -0,0 +1,83 @@
+package at.test.drm;
+
+import com.google.testing.compile.Compilation;
+import com.google.testing.compile.CompilationSubject;
+import com.google.testing.compile.Compiler;
+import com.google.testing.compile.JavaFileObjects;
+import org.junit.jupiter.api.Test;
+
+import javax.tools.JavaFileObject;
+
+import static com.google.common.truth.Truth.assertThat;
+
+class RelationProcessorTest {
+
+    @Test
+    void shouldGenerateCodeForRelationAnnotation() {
+
+        // 1. Fake input class
+        JavaFileObject source = JavaFileObjects.forSourceString(
+                "test.User",
+                """
+                package test;
+
+                import at.drm.annotation.Relation;
+
+                @Relation
+                public class User {
+                }
+                """
+        );
+
+        // 2. Run processor
+        Compilation compilation = Compiler.javac()
+                .withProcessors(new at.drm.processor.RelationProcessor())
+                .compile(source);
+
+        // 3. Assert compilation success
+        assertThat(compilation.status())
+                .isEqualTo(Compilation.Status.SUCCESS);
+
+        // 4. Assert something was generated
+        assertThat(compilation.generatedSourceFiles())
+                .isNotEmpty();
+
+        // 5. Get generated file content
+        String generated = String.valueOf(CompilationSubject.assertThat(compilation)
+                .generatedSourceFile("test.UserRelation")
+                .contentsAsUtf8String());
+
+        // 6. Strong assertions
+        assertThat(generated).contains("package test;");
+        assertThat(generated).contains("class UserRelation");
+    }
+
+
+    @Test
+    void shouldNotGenerateWhenAnnotationMissing() {
+
+        // 1. Input WITHOUT @Relation
+        JavaFileObject source = JavaFileObjects.forSourceString(
+                "test.User",
+                """
+                package test;
+
+                public class User {
+                }
+                """
+        );
+
+        // 2. Run processor
+        Compilation compilation = Compiler.javac()
+                .withProcessors(new at.drm.processor.RelationProcessor())
+                .compile(source);
+
+        // 3. Should still compile successfully
+        assertThat(compilation.status())
+                .isEqualTo(Compilation.Status.SUCCESS);
+
+        // 4. But should NOT generate any files
+        assertThat(compilation.generatedSourceFiles())
+                .isEmpty();
+    }
+}