[Solved] IllegalStateException: Could not initialize plugin MockMaker

If you are working on Spring boot 2.x applications which automatically includes Mockito Core dependency and you are facing this error, then you may try the solution suggested.

  • The root cause of this error is the version mismatch between Mockito and ByteBuddy.
  • For a few people, it turned out to be JDK configuration. Make sure the IDE is pointing to a JRE. It should be a JDK path.

1. Problem

Mockito core depends on a library called byte-buddy and this problem mostly occurs when mockito doesn’t find a matching byte buddy jar version. The error looks like this:

java.lang.IllegalStateException: Could not initialize plugin: interface org.mockito.plugins.MockMaker (alternate: null)
	at org.mockito.internal.configuration.plugins. PluginLoader$1.invoke(PluginLoader.java:74) ~[mockito-core-2.23.4.jar:na]
	at com.sun.proxy.$Proxy61.getHandler(Unknown Source) ~[na:na]
	at org.mockito.internal.util. MockUtil.isMock(MockUtil.java:81) ~[mockito-core-2.23.4.jar:na]
	...
	...
Caused by: java.lang.NoClassDefFoundError: net/bytebuddy/dynamic/loading/ ClassInjector$UsingReflection
	at org.mockito.internal.creation.bytebuddy. SubclassInjectionLoader.<init>(SubclassInjectionLoader.java:28) ~[mockito-core-2.23.4.jar:na]
	at org.mockito.internal.creation.bytebuddy. SubclassByteBuddyMockMaker.<init>(SubclassByteBuddyMockMaker.java:33) ~[mockito-core-2.23.4.jar:na]
	at org.mockito.internal.creation.bytebuddy. ByteBuddyMockMaker.<init>(ByteBuddyMockMaker.java:21) ~[mockito-core-2.23.4.jar:na]

	...
	...
	[spring-test-5.1.4.RELEASE.jar:5.1.4.RELEASE]
	... 19 common frames omitted
Caused by: java.lang.ClassNotFoundException: net.bytebuddy.dynamic. loading.ClassInjector$UsingReflection
	at java.net.URLClassLoader.findClass(Unknown Source) ~[na:1.8.0_171]
	at java.lang.ClassLoader.loadClass(Unknown Source) ~[na:1.8.0_171]
	at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source) ~[na:1.8.0_171]
	at java.lang.ClassLoader.loadClass(Unknown Source) ~[na:1.8.0_171]
	... 42 common frames omitted

2. Solution

Find out the mockito core version your project is using. In eclipse, you can check-in project build path by navigating to

Right click on project -> Properties -> Java build path -> Libraries tab

Mockito core dependency
Mockito core dependency

Search maven repository for that version of mockito core. To me, it was: https://mvnrepository.com/artifact/org.mockito/mockito-core/2.23.4

Look at the Compile Dependencies section. Note down the correct dependent version of byte-buddy and include in the project. If the jar is already included with some other version, override the version with this correct version.

Correct jar version
Correct jar version

Build the application and run the tests again. Your issue related to MockMaker must be solved by now.

Happy Learning !!

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