주문 생성시 상품 중복 제거 로직 질문입니다.

Business Layer 테스트(2)강의 3:54부터 나온 중복 제거 로직이 저렇게 돌아가는건지 궁금해서 private 메서드 public으로 열고

간단한 테스트 작성하고 브레이크 포인트 잡아서 실행해봤는데

이런 에러가 나오네용..

밑에는 에러 로그입니다.

```
Duplicate key 001 (attempted merging values sample.cafekiosk.spring.domain.product.Product@5d10e2b6 and sample.cafekiosk.spring.domain.product.Product@1de6689c)

java.lang.IllegalStateException: Duplicate key 001 (attempted merging values sample.cafekiosk.spring.domain.product.Product@5d10e2b6 and sample.cafekiosk.spring.domain.product.Product@1de6689c)

at java.base/java.util.stream.Collectors.duplicateKeyException(Collectors.java:133)

at java.base/java.util.stream.Collectors.lambda$uniqKeysMapAccumulator$1(Collectors.java:180)

at java.base/java.util.stream.ReduceOps$3ReducingSink.accept(ReduceOps.java:169)

at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1655)

at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)

at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)

at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913)

at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)

at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578)

at sample.cafekiosk.spring.api.service.order.OrderService.findProductsBy(OrderService.java:44)

at sample.cafekiosk.spring.api.service.order.OrderServiceTest.mapTest(OrderServiceTest.java:205)

at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)

at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

at java.base/java.lang.reflect.Method.invoke(Method.java:566)

at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:725)

at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)

at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)

at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:149)

at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:140)

at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:84)

at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115)

at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105)

at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)

at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64)

at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45)

at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37)

at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:104)

at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98)

at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$7(TestMethodTestDescriptor.java:214)

at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)

at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:210)

at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:135)

at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:66)

at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:151)

at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)

at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)

at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)

at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)

at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)

at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)

at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)

at java.base/java.util.ArrayList.forEach(ArrayList.java:1541)

at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)

at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155)

at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)

at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)

at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)

at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)

at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)

at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)

at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)

at java.base/java.util.ArrayList.forEach(ArrayList.java:1541)

at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:41)

at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$6(NodeTestTask.java:155)

at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)

at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:141)

at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)

at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$9(NodeTestTask.java:139)

at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)

at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:138)

at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:95)

at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:35)

at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)

at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:54)

at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:107)

at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:88)

at org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:54)

at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:67)

at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:52)

at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:114)

at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:86)

at org.junit.platform.launcher.core.DefaultLauncherSession$DelegatingLauncher.execute(DefaultLauncherSession.java:86)

at org.junit.platform.launcher.core.SessionPerRequestLauncher.execute(SessionPerRequestLauncher.java:53)

at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor$CollectAllTestClassesExecutor.processAllTestClasses(JUnitPlatformTestClassProcessor.java:99)

at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor$CollectAllTestClassesExecutor.access$000(JUnitPlatformTestClassProcessor.java:79)

at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor.stop(JUnitPlatformTestClassProcessor.java:75)

at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.stop(SuiteTestClassProcessor.java:62)

at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)

at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

at java.base/java.lang.reflect.Method.invoke(Method.java:566)

at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:36)

at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)

at org.gradle.internal.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:33)

at org.gradle.internal.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:94)

at com.sun.proxy.$Proxy2.stop(Unknown Source)

at org.gradle.api.internal.tasks.testing.worker.TestWorker$3.run(TestWorker.java:193)

at org.gradle.api.internal.tasks.testing.worker.TestWorker.executeAndMaintainThreadName(TestWorker.java:129)

at org.gradle.api.internal.tasks.testing.worker.TestWorker.execute(TestWorker.java:100)

at org.gradle.api.internal.tasks.testing.worker.TestWorker.execute(TestWorker.java:60)

at org.gradle.process.internal.worker.child.ActionExecutionWorker.execute(ActionExecutionWorker.java:56)

at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.call(SystemApplicationClassLoaderWorker.java:113)

at org.gradle.process.internal.worker.child.SystemApplicationClassLoaderWorker.call(SystemApplicationClassLoaderWorker.java:65)

at worker.org.gradle.process.internal.worker.GradleWorkerMain.run(GradleWorkerMain.java:69)

at worker.org.gradle.process.internal.worker.GradleWorkerMain.main(GradleWorkerMain.java:74)
```
검색해보니까 "Collectors.toMap() 호출에서 세 번째 파라미터로 중복된 키의 값을 핸들링하는 람다식이 제공되지 않았기 때문에 발생합니다."라고 하는데요.

신기하게도 저렇게 말고 원래 작성해주신 코드의 테스트로 실행하면 잘 작동을 하네요.

왜 그런건지 여쭤봐도 될까요?