Use statically-defined test class tags

[FWDekker]

Instead of using NamedTag(...) separately in each test class, collect all possible tags centrally in, say, TestTags, and refer to those.

This will make it easier to know which tags are available, and to check their usages to see if anything is missing or incorrect.

[FWDekker]

And while I'm at it, replace shouldBe null with should beNull(), for consistency.

[FWDekker]

Oh, and change shouldBe Bundle(...) to should matchBundle(...)!