How do I step into the source code of the JUnit plugin in IntelliJ?

Question

When I run my test in debugging mode in IntelliJ (2017.2 Community Edition), the source code is only available for some of the code.

In particular, when I step through code in the package com.intellij.junit4, the debugger shows the method name and line number in the stack view, but the code doesn't appear in the editor.

Answer 1

You need to add the jar containing the source code to the class path of the project. The jar is located at the path plugins/junit/lib/junit-rt.jar relative to the folder that IntelliJ is installed into.

Go to "Project Structure" > "Libraries" > "+" > "Java" and add the path of the Jar.

See also this answer.