Fix build.

backend/build.gradle.kts

@@ -32,6 +32,8 @@ subprojects {
         testImplementation("org.assertj:assertj-core:3.27.4")
         testImplementation("org.junit.jupiter:junit-jupiter-api")
         testImplementation("org.junit.jupiter:junit-jupiter-params")
+        testImplementation("org.springframework.boot:spring-boot-starter-test")
+        testImplementation("org.junit.platform:junit-platform-launcher")
     }
 
     tasks.withType<Test> {