Setting environment fails on Java 17-ea

I have a few tests using the @SetEnvironmentVariable annotation. Unfortunately, at the moment, they fail on Java 17 (EA) with:

java.lang.reflect.InaccessibleObjectException: Unable to make field private static final java.util.HashMap java.lang.ProcessEnvironment.theEnvironment accessible: module java.base does not "opens java.lang" to unnamed module @527b7298

[Michael1993]

There is really no nicer way to say this: you should have read the documentation. Here is the relevant section:

Warnings for Reflective Access

As explained above, this extension uses reflective access to change the otherwise immutable environment variables. On Java 9 to 16, this leads to a warning like the following:

[ERROR] WARNING: An illegal reflective access operation has occurred
[ERROR] WARNING: Illegal reflective access by org.junitpioneer.jupiter.EnvironmentVariableUtils [...] to field [...]
[ERROR] WARNING: Please consider reporting this to the maintainers of org.junitpioneer.jupiter.EnvironmentVariableUtils
[ERROR] WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
[ERROR] WARNING: All illegal access operations will be denied in a future release

On Java 17 and later, you get this error instead:

java.lang.reflect.InaccessibleObjectException: Unable to make field [...] accessible:
module java.base does not "opens java.lang" to unnamed module [...]

The best way to prevent these warnings/errors, is to change the code under test, so this extension is no longer needed. The next best thing is to allow access to that specific package with --add-opens=java.base/java.util=ALL-UNNAMED (if you place JUnit Pioneer on the class path) or --add-opens=java.base/java.util=org.junitpioneer (if you place it on the module path).

These command line options need to be added to the JVM that executes the tests:

• Gradle
• Maven basics and advanced

[ashleyfrieze]

This issue could be solved - see https://github.com/webcompere/system-stubs/blob/main/system-stubs-core/src/main/java/uk/org/webcompere/systemstubs/environment/EnvironmentVariableMocker.java

The solution involves depending on mockito-inline, but is easily adopter. You could reasonably copy the above code, or could add the above as a dependency for JUP.

I’m the author of the above class, so feel free to use it as you wish.