How can a private class method be tested in Scala?

Question

I have a companion object with a private method, like so:

package com.example.people  class Person(val age: Int)  object Person {   private def transform(p: Person): Person = new Person(p.age + 1) } 

I would like to test this method, with something like:

class PersonSpec extends FlatSpec {    "A Person" should "transform correctly" in {     val p1 = new Person(1)     val p2 = Person.transform(p1) // doesn't compile, because transform is private!     assert( p2 === new Person(2) )   }  } 

Any help on having test code access private methods?

Actually, as it is written, I might be able to create a subclass of Person, but what if Person is declared as final or sealed?

Thanks!

Answer 1

I am in the middle when it comes to testing everything. I don't usually test everything, but sometimes it's really useful to be able to unit test a private function without having to mangle my code to make it possible. If you're using ScalaTest, you can use the PrivateMethodTester to do it.

import org.scalatest.{ FlatSpec, PrivateMethodTester }  class PersonSpec extends FlatSpec with PrivateMethodTester {    "A Person" should "transform correctly" in {       val p1 = new Person(1)       val transform = PrivateMethod[Person]('transform)       // We need to prepend the object before invokePrivate to ensure       // the compiler can find the method with reflection       assert(p2 === p1 invokePrivate transform(p1))     }   } 

That may not be exactly what you want to do, but you get the idea.