JUnit5 test classes and methods should have default package visibility

…ion.

… of simple "instanceof"

…ility

… pass the values directly.

Field dependency injection should be avoided

…ility

…ned or thrown

… of simple "instanceof" + cast

…rializable

…ce()"

Generic wildcard types should not be used in return types

…am.toList()'

"Stream.toList()" method should be used instead of "collectors"
when unmodifiable list needed

…ld also override "equals"