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Cannot mock wrapper types, String.class or Class.class #1734

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moleksyuk opened this issue Jun 26, 2019 · 1 comment
Closed

Cannot mock wrapper types, String.class or Class.class #1734

moleksyuk opened this issue Jun 26, 2019 · 1 comment
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@moleksyuk
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@moleksyuk moleksyuk commented Jun 26, 2019

Hi,
Mockito can't not mock String.class even with org.mockito:mockito-inline:2.28.2, but mocks custom final classes successfully.

Version:
JUnit: org.junit.jupiter:junit-jupiter:5.4.2
Mockito-core: org.mockito:mockito-core:2.28.2
Mockito-inline: org.mockito:mockito-inline:2.28.2

Steps to reproduce:

  1. Download example project and unzip it: mockito.zip
  2. Go to project directory and execute such command:
./gradlew clean build

Actual result:



Cannot mock/spy class java.lang.String
Mockito cannot mock/spy because :
 - Cannot mock wrapper types, String.class or Class.class
org.mockito.exceptions.base.MockitoException: 
Cannot mock/spy class java.lang.String
Mockito cannot mock/spy because :
 - Cannot mock wrapper types, String.class or Class.class
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:628)
	at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:117)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$7(TestMethodTestDescriptor.java:184)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:180)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:127)
	at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:68)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:135)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
	at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
	at java.util.ArrayList.forEach(ArrayList.java:1257)
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
	at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
	at java.util.ArrayList.forEach(ArrayList.java:1257)
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
	at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
	at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
	at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
	at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32)
	at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
	at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51)
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:170)
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:154)
	at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:90)
	at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor$CollectAllTestClassesExecutor.processAllTestClasses(JUnitPlatformTestClassProcessor.java:92)
	at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor$CollectAllTestClassesExecutor.access$100(JUnitPlatformTestClassProcessor.java:77)
	at org.gradle.api.internal.tasks.testing.junitplatform.JUnitPlatformTestClassProcessor.stop(JUnitPlatformTestClassProcessor.java:73)
	at org.gradle.api.internal.tasks.testing.SuiteTestClassProcessor.stop(SuiteTestClassProcessor.java:61)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:35)
	at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
	at org.gradle.internal.dispatch.ContextClassLoaderDispatch.dispatch(ContextClassLoaderDispatch.java:32)
	at org.gradle.internal.dispatch.ProxyDispatchAdapter$DispatchingInvocationHandler.invoke(ProxyDispatchAdapter.java:93)
	at com.sun.proxy.$Proxy2.stop(Unknown Source)
	at org.gradle.api.internal.tasks.testing.worker.TestWorker.stop(TestWorker.java:131)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:35)
	at org.gradle.internal.dispatch.ReflectionDispatch.dispatch(ReflectionDispatch.java:24)
	at org.gradle.internal.remote.internal.hub.MessageHubBackedObjectConnection$DispatchWrapper.dispatch(MessageHubBackedObjectConnection.java:155)
	at org.gradle.internal.remote.internal.hub.MessageHubBackedObjectConnection$DispatchWrapper.dispatch(MessageHubBackedObjectConnection.java:137)
	at org.gradle.internal.remote.internal.hub.MessageHub$Handler.run(MessageHub.java:404)
	at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:63)
	at org.gradle.internal.concurrent.ManagedExecutorImpl$1.run(ManagedExecutorImpl.java:46)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:55)
	at java.lang.Thread.run(Thread.java:748)

Expected result: test with mock for String.class is passed.

@TimvdLippe
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@TimvdLippe TimvdLippe commented Jun 26, 2019

This is working as intended. You can't mock strings. Use a real string instead.

@TimvdLippe TimvdLippe closed this Jun 26, 2019
@bric3 bric3 added the question label Jul 2, 2019
TimvdLippe added a commit that referenced this issue Nov 28, 2019
Mocking types that users not own [1] or are severely complicating test
logic [2] leads to brittle or wrong tests. In particular, the
StackOverflow answer is wrong, as the contract of java.util.Map is
violated. When a new key is added to the Map, the stubbed return would be wrong.
In Google we have used the DoNotMock annotation via ErrorProne [3]
to annotate these types, as well as an internal list of types that can't
be mocked (this includes several java.util types). We are using a custom
Mockmaker to enforce this on run-time.

Based on our successful experience with DoNotMock (we have seen a large
reduction in bad/broken tests for types involved), we are proposing to
open source this into Mockito itself.

The DoNotMock annotation can be added to any type, e.g. classes and
interfaces. If, in the type hierarchy of the class-to-be-mocked, there
is a type that is annotated with DoNotMock, Mockito will throw a
DoNotMockException.

This would help preventing issues such as #1827 and #1734 which is
in-line with the guidance on our wiki [1]. A follow-up change would
allow us to define external types (like the java.util types) that can't
be mocked. (We can't add the annotation to the types, as they live in the
JDK instead.)

[1]: https://github.com/mockito/mockito/wiki/How-to-write-good-tests#dont-mock-a-type-you-dont-own
[2]: https://stackoverflow.com/a/15820143
[3]: https://errorprone.info/api/latest/com/google/errorprone/annotations/DoNotMock.html
TimvdLippe added a commit that referenced this issue Nov 19, 2021
Mocking types that users not own [1] or are severely complicating test
logic [2] leads to brittle or wrong tests. In particular, the
StackOverflow answer is wrong, as the contract of java.util.Map is
violated. When a new key is added to the Map, the stubbed return would be wrong.
In Google we have used the DoNotMock annotation via ErrorProne [3]
to annotate these types, as well as an internal list of types that can't
be mocked (this includes several java.util types). We are using a custom
Mockmaker to enforce this on run-time.

Based on our successful experience with DoNotMock (we have seen a large
reduction in bad/broken tests for types involved), we are proposing to
open source this into Mockito itself.

The DoNotMock annotation can be added to any type, e.g. classes and
interfaces. If, in the type hierarchy of the class-to-be-mocked, there
is a type that is annotated with DoNotMock, Mockito will throw a
DoNotMockException.

This would help preventing issues such as #1827 and #1734 which is
in-line with the guidance on our wiki [1]. A follow-up change would
allow us to define external types (like the java.util types) that can't
be mocked. (We can't add the annotation to the types, as they live in the
JDK instead.)

This PR also introduces the DoNotMockEnforcer interface which users can override
to implement their special handling of types annotated with DoNotMock.

[1]: https://github.com/mockito/mockito/wiki/How-to-write-good-tests#dont-mock-a-type-you-dont-own
[2]: https://stackoverflow.com/a/15820143
[3]: https://errorprone.info/api/latest/com/google/errorprone/annotations/DoNotMock.html
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