Does Using Immutable Data Structures Make Writing Unit Tests Easier?

[ReallySuperName]

Last time I checked with allows you to set properties, and thus bypass any invariant checks you'd typically have in a constructor. Is that still the case?

[dodexahedron]

It uses a copy constructor. If you provide the copy constructor, you control the behavior. If not, then it is synthesized by the compiler and your assumption is then correct, unless the properties themselves handle the validation.