restrict PHPUnit to 9.5 version

There are so many breaking changes with PHPUnit that it is
impossible to give any other guarantees.

diff --git a/docs/develop/Development-Environment.md b/docs/develop/Development-Environment.md
index 2840095b8615e6cfc8bd94ed0bb51c346d262dd5..eba87c09e68138e20b08fdacb3f9139a8efd1345 100644 (file)
--- a/docs/develop/Development-Environment.md
+++ b/docs/develop/Development-Environment.md
@@ -30,7 +30,7 @@ unit tests (using PHPUnit for PHP code and pytest for Python code).
 It has the following additional requirements:
 
 * [behave test framework](https://behave.readthedocs.io) >= 1.2.6
-* [phpunit](https://phpunit.de) >= 7.3
+* [phpunit](https://phpunit.de) (9.5 is known to work)
 * [PHP CodeSniffer](https://github.com/squizlabs/PHP_CodeSniffer)
 * [Pylint](https://pylint.org/) (2.6.0 is used for the CI)
 * [pytest](https://pytest.org)