Add method for performing assertions as part of an at check.

[ldaley]

This is primarily for getting better IDE autocomplete. The following could be added to Browser…

<T extends Page, R> R at(T pageType, @DelegatesTo("T") Closure<R> assertions) {}

The implicit assertion transform would be applied to the closure body.

Usage would look like:

then:
at(SomePage) {
  somePageProperty == "foo"
}

In IDEA at least, you should get completion for the page properties in the closure body due to the use of DelegatesTo.