License compatibility with GPL

[dbrgn]

Hello team!

JUnit 4 is published under the EPL 1.0 license. This license is incompatible with the GPL license family.

In #1045, before the release of JUnit 5, the license was changed to the EPL 2.0. This license can be made compatible with the GPL license family by listing it as a secondary license. However, by default it does not include this compatibility.

In that referenced issue, @sbrannen notes that "(...) we have learned that the JUnit Team does not need to seek the permission of past contributors, unless the team wants to add in the GPL compatibility" (emphasis mine). The license was then changed, as far as I can tell without asking previous contributors. Additionally, I cannot find any secondary licenses mentioned in the README or LICENSE.md files.

Would it be possible to clarify whether or not JUnit 5+ is compatible with the GPL license family? From the information I gathered so far, I would think that it is not currently compatible, and may not be redistributed in a codebase that is licensed under the GPL.

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As an extension of the question above (which primarily concerns compatibility): For most developers using JUnit, the question will not be about modification or extension of JUnit, but insetad about writing JUnit tests. From how I understand the EPL, it is a file-level copyleft license. This means that: As long as I don't modify JUnit files themselves, I can write and redistribute tests against JUnit, even if these tests are licensed under the GPL or under proprietary licenses. And I can distribute binaries under the GPL license, as long as these don't contain the JUnit code (binaries usually don't contain any tests).

However, I am not a lawyer. Do you have the possibility of confirming this interpretation of the license?