Extensions have to be stateless

[asarkar]

From JUnit 5 Extension Model:

The engine makes no guarantees when it instantiates extensions and how long it keeps instances around. This has a number of reasons:

It is not clear when and how extensions should be instantiated. (For each test? For each class? For each run?)
Jupiter does not want to bother tracking extension instances.
If extensions were to communicate with one another, a mechanism for exchanging data would be required anyways.
Hence, extensions have to be stateless. Any state they need to maintain has to be written to and loaded from the store that the extension context makes available.