Offline Jacoco using MockStatic cause re-instrumentation exception - mockito

Question

I'm running PowerMock 1.6.4 and all the latest (JUnit 4.11 though).
I use the Jacoco Ant task to only instrument the classes, not the test classes. I also use the Jacoco ant task to run the Junit tests, then generate the reports.
Now I'm hitting a problem that I can't figure out...
I have a test class that tests one member function of class Foo.
One of the members of Foo is static, so I've wrapped that in a static function so I can control the execution via mock but the side effect is that I need to mockStatic now.
What I've noticed is that PowerMockito.mockStatic(Foo.class) ... all tests fail with instrumentation problems.
I have another test class that tests another member function of Foo. This test class works fine, but as soon as I introduce a mockStatic the test class fails with instrumentation failures.
Has anyone see this failure and know of any workarounds? I can't change the static member variable.

Answer 1

I finally figured out what I believe is the issue. Jacoco instrumentation injects data into your byte code so does PowerMock when it attempts to mock statics. This wrecks havoc since they are stepping on each other and you will get really odd behavior due to them messing with each other. I was getting an assorted bunch of NPE's in code that shouldn't throw NPE's.
The easy solution was to refactor out the unnecessary statics and know that if you plan to use statics to control data flow, probably should rethink the architecture for testing if you plan to use Jacoco for coverage.
You can still run Jacoco instrumentation on statics but you can't mock statics at the same time; at least not with the way PowerMock with Mockito does it. I'm not sure if EasyMock would result in a different behavior, so ymmv.

Answer 2

I had similar issues, but instead of having to refactor the statics out I believe there is another solution. I did this in a maven pom file but I'll explain what is going on. Jacoco does inject data into your byte code. And yes Powermock uses a custom Byte loader and Jacoco hates that. So heres a solution to work around it.
In your Jacoco executions, you need Jacoco to use default-instrumentation for your tests. (you can specify powermock tests or just include all tests it works either way). Heres an explantion of whats going on with default-Instrumentation: Offline-instrumentation with Jacoco.
You must then have the restore step for the tests. Now heres the interesting part, you have to run the normal Jacoco Prepare Agent step, while EXCLUDING all the tests that were run in default instrumentation. (if you don't you will get a bunch of warnings something like JaCoCo exceution data already exists for xTest)
This will solve your problem, and you don't need to refactor out your static methods. Though if they were unnecessary you should probably still take them out ;)
<plugin>
<groupId>org.jacoco</groupId>
<artifactId>jacoco-maven-plugin</artifactId>
<version>${jacoco.version}</version>
<configuration>
<append>true</append>
</configuration>
<executions>
<execution>
<id>default-instrument</id>
<goals>
<goal>instrument</goal>
</goals>
<configuration>
<includes>
<include>**/*test*</include>
</includes>
</configuration>
</execution>
<execution>
<id>default-restore-instrumented-classes</id>
<goals>
<goal>restore-instrumented-classes</goal>
</goals>
<configuration>
<includes>
<include>**/*test*</include>
</includes>
</configuration>
</execution>
<execution>
<id>Prepare-Jacoco</id>
<goals>
<goal>prepare-agent</goal>
</goals>
<configuration>
<excludes>
<exclude>**/*test*</exclude>
</excludes>
</configuration>
</execution>
</executions>
</plugin>