Testing a unit with implicit class in Scala -

imagine have service:

class servicea(serviceb: serviceb) {     import extractor._     def send(typea: a) = serviceb.send(typea.extract)  }  object extractor {    implicit class extractor(type: a) {       def extract = ???    } } 

i want extract method implicitly defined because doesn't directly relate a type/domain , solution specific adhoc extension.

now write simple unit test confirms serviceb.send called.

for that, mock service , pass mocked a send. assert serviceb.send called mocked a.

as seen in example, send method transformation on typea parameter need mock extract method return specified value. however, a doesn't have extract method - comes implicit class.

so question - how mock out implicit class in example above imports not first class citizens.

if want specify bunch of customised extract methods, can this:

sealed trait extractor[t] {   // or whatever signature want   def extract(obj: t): string } object extractor {    implicit case object intextractor extends extractor[int] {     def extract(obj: int): string = s"i int , value $obj"   }   implicit case object stringextractor extends extractor[string] {     def extract(obj: string): string = s"i "   }    def apply[a : extractor](obj: a): string = {     implicitly[extractor[a]].extract(obj)   }  } 

so have sealed type family that's pre-materialised through case objects, arguably useful in match. let decouple everything.

if don't want mix extractor, call them else , follow same approach, can mix in context bound.

then can use with:

println(extractor(5)) 

for testing, override available implicits if need to. bit of work, not impossible, can control scope , can spy on whatever method calls want.

e.g instead of import extractor._ have other object test logic can use mocks or alternative implementation.