In Groovy, non-zero integers, non-null values, nonempty strings, initialized collections, and a valid matcher are evaluated as Boolean true values. This is known as Groovy Truths

the closure will try to resolve the property or methods to the delegate first and then the owner.

It attempts to resolve the property or methods within the owner only and doesn't delegate

Closure will resolve the property references or methods to the delegate. It completely ignores the owner

It will resolve the property references or methods to itself and go through the usual MetaClass look-up process