Mockito 2 final class mocking limitations

[Andrew Audibert]

Hi all,

Our team has run into many issues with PowerMock due to its replacing the system classloader. I'm excited to see that core Mockito is coming out with its own way of mocking final classes. Does the Mockito approach also rely on modifying the classloader? The 2.1 announcement mentions

Mocking of final classes and methods is an incubating, opt-in feature. It uses a combination of Java agent instrumentation and subclassing in order to enable mockability of these types. As this works differently to our current mechanism and this one has different limitations and as we want to gather experience and user feedback, this feature had to be explicitly activated to be available

Can anyone expand on what these different limitations are? 

Thanks,

Andrew Audibert

[Tim van der Lippe]

Hello Andrew,

While the Javadoc is not available on the site, we listed the limitations in the Javadoc of the new MockMaker: https://github.com/mockito/mockito/blob/release/2.x/src/main/java/org/mockito/internal/creation/bytebuddy/InlineByteBuddyMockMaker.java#L67-L73 

You can not mock native methods and can no longer strip synchronized modifiers from mocked instances. Package-visible methods will not be mocked by the new mockmaker.

Hope that answers your question.

Enjoy mocking with Mockito 2!

Tim

Op do 27 okt. 2016 om 11:01 schreef Andrew Audibert <aaudi...@gmail.com>:

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[Brice Dutheil]

Hi Andrew,

Thanks for the Mockito final class excitement :) Keep in mind this is still experimental.

Powermock used clever technics with the classloader and plugged in the internals of mockito, however they said they are not enough contributors and that they have not enough time to make Powermock compatible with mockito 2 at this time.

On a project with my client I completely removed Powermock.

As you have read below mockito rely on instrumentation. That means that mockito 2 does not need to play with classloader at all.

The limitations are listed on the Mockito class : http://static.javadoc.io/org.mockito/mockito-core/2.2.7/org/mockito/Mockito.html#Mocking_Final

Quoted here :

Some noteworthy notes about this mock maker:

• Mocking final types and enums is incompatible with mock settings like :
  • explicitly serialization support withSettings().serializable()
  • extra-interfaces withSettings().extraInterfaces()
• Some methods cannot be mocked
  • Package-visible methods of java.*
  • native methods
• This mock maker has been designed around Java Agent runtime attachment ; this require a compatible JVM, that is part of the JDK (or Java 9 VM). When running on a non-JDK VM prior to Java 9, it is however possible to manually add the Byte Buddy Java agent jar using the -javaagentparameter upon starting the JVM.

-- Brice

_____________________________
From: Andrew Audibert <aaudi...@gmail.com>
Sent: Thursday, October 27, 2016 11:01
Subject: [mockito] Mockito 2 final class mocking limitations
To: mockito <moc...@googlegroups.com>

--

[Brice Dutheil]

Seems that Tim raced me ;)

[Bartosz Miller]

Hi Tim,

I started to play with mocking final classes, tried to mock String.class and ... fail! 

I noticed in the source that the following list of classes in excluded from mocking: 

Class.class, Boolean.class, Byte.class, Short.class, Character.class, Integer.class, Long.class, Float.class, Double.class, String.class

What is the technical reason of that?

Regards,

Bartosz

[Brice Dutheil]

They have special handling in the JDK itself. Messing with those break the JDK.

-- Brice

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[David Karr]

What is your technical reason for wanting to mock String?

> https://groups.google.com/d/msgid/mockito/9565ccd9-bffe-4d35-a9a4-491fe2dec12e%40googlegroups.com.

[Brice Dutheil]

The same, it breaks your JDK runtime.

-- Brice

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[David Karr]

To be clear, I'm asking the OP why he's even attempting to mock
String. That could short-circuit these attempts to mock things that
are unmockable.

>> > https://groups.google.com/d/msgid/mockito/9565ccd9-bffe-4d35-a9a4-491fe2dec12e%40googlegroups.com.
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[Marcin Grzejszczak]

Hi Bartosz,

can you show a sample of your code so that we can understand what you want to do? What you're doing sounds like a terrible antipatern.