FeatureWithCreator(description: String, extractor: (T) -> R, assertionCreator: Expect<R>.() -> Unit)
Parameter object which contains a description of a feature along with an extractor which actually extracts the feature out of a subject of an assertion + an assertionCreator which defines assertions for the feature.
Use of(K..., ...) { ... } to create this representation where the first argument is the extractor in form of a
KProperty1 or a KFunctionX, the last an assertionCreator-lambda and the remaining arguments in-between the
required arguments in case of a KFunctionX where X > 1.