Testing a private method with access modifier in Scalatest

Question

I have the following issue.

Suppose I have the following class (example from here: Link ):

package com.example.people

class Person(val age: Int)

object Person {
  private def transform(p: Person): Person = new Person(p.age + 1)
}

So I have a package, and inside it I have a class with a private method.

Now I know using scalatest I can do something like this. In my test folder I have:

import org.scalatest.{ FlatSpec, PrivateMethodTester }

class PersonTest extends AnyFunSuite with PrivateMethodTester {

  test("A Person" should "transform correctly") {
      val p1 = new Person(1)
      val transform = PrivateMethod[Person]('transform)
      assert(p2 === p1 invokePrivate transform(p1))
    }
  }

Now, my question is, if I add an access modifier to my private method as follows (similar to the answer in this Link):

package com.example.people

class Person(val age: Int)

object Person {
  private[example] def transform(p: Person): Person = new Person(p.age + 1)
}

The test complains that transform is no longer a private method.

Is there a way I can still use the private method tester, even if I have an access modifier for a private function?

Why do you need the private method tester if the method is no longer private? Just call it directly. — Thilo, Jul 11 '20 at 11:15
Thanks @Thilo, the reason is my test suite is not in the example package, but as Mario mentioned below, I can just add the test to the package. — finite_diffidence, Jul 11 '20 at 11:29
Tests should always be in the same package as the class they are testing. And you shouldn't need to test private methods. — Luis Miguel Mejía Suárez, Jul 11 '20 at 15:03

score 3 · Accepted Answer · answered Jul 11 '20 at 11:11

3

Given

package com.example.people

class Person(val age: Int)

object Person {
  private[example] def transform(p: Person): Person = new Person(p.age + 1)
}

you just have to make sure that corresponding test is also within example package

package example

class PersonTest extends AnyFunSuite {
  test("A Person should transform correctly") {
    val p1 = new Person(1)
    Person.transform(p1)    // transform is now accessible
    ...
    }
  }
}

in which case there is no need for PrivateMethodTester because private[example] makes the method available to all the members of example package.

answered Jul 11 '20 at 11:11

Mario Galic

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Thanks @Mario, but if I add my tests to package example, wouldn't users of my library be able to access personTest? Is there a way to prevent users from doing so? – finite_diffidence Jul 11 '20 at 11:30
2

@finite_diffidence Sources under `src/test/scala` should not end up in the packaged/assambled jar. Also note, in general, it is good practice to have tests mirror the package structure of main sources – Mario Galic Jul 11 '20 at 11:40
Doing so, it is making the def public for all `example` package, in main and test sources. So the goal of `private` is almost completly lost here. The question is still open for me: how can we test a private fonction ? – Quentame Mar 01 '23 at 14:26
It's like Java's `package` – Quentame Mar 01 '23 at 15:00

Testing a private method with access modifier in Scalatest

1 Answers1