How to test non-public methods?

Question

I am learning Scala and wrote Email class which looks like:

class Email(emailConfigName: String) {
  private val emailConfig = ConfigFactory.load(emailConfigName) getConfig ("email")

  def notifySupportForTenant(symbolicName: String) {
    val emailMessage: Message = constructEmailMessage(symbolicName)
    Transport.send(emailMessage)
  }

  def constructEmailMessage(symbolicName: String): Message = {
    val message = createMessage(emailConfig getString ("shn.mail.smtp.host"))
    message setFrom (new InternetAddress(emailConfig getString ("shn.mail.from")))
    // todo: should come from API (sent by client)
    message setSentDate (new Date())
    message setSubject (emailConfig getString ("shn.mail.subject") replace("TENANT_ID", symbolicName))
    message setContent(emailConfig getString ("shn.mail.body"), "text/html")
    message.setRecipients(Message.RecipientType.TO, getMessageRecipients(emailConfig getString ("shn.mail.recipient")))
    message
  }

  private def createMessage(smtpHost: String): Message = {
    val properties = new Properties()
    properties put("mail.smtp.host", smtpHost)
    val session = Session.getDefaultInstance(properties, null)
    return new MimeMessage(session)
  }

  private def getMessageRecipients(recipient: String): Array[Address] = {
    // had to do the asInstanceOf[...] call here to make scala happy
    val addressArray = buildInternetAddressArray(recipient).asInstanceOf[Array[Address]]
    if ((addressArray != null) && (addressArray.length > 0)) addressArray
    else
      throw new IllegalArgumentException("no recipients found to send email")
  }

  private def buildInternetAddressArray(address: String): Array[InternetAddress] = {
    // could test for a null or blank String but I'm letting parse just throw an exception
    return InternetAddress.parse(address)
  }
}

I want to test this class's public API, notifySupportForTenant but this is not good for unit test since it also calls Transport.send(emailMessage) which will send the email.

All I am interested in testing if the message is constructed correctly. Which means I need to test constructEmailMessage.

In order to test this, I had to make this public which is also exposed as public interface, which I do not prefer. What can I do?

One common way out is to make the private methods package-private, and then put the tests in the same package. — Seth Tisue, Jul 30 '15 at 22:05
possible duplicate of [How to test a class that has private methods, fields or inner classes](http://stackoverflow.com/questions/34571/how-to-test-a-class-that-has-private-methods-fields-or-inner-classes) — Egor, Jul 30 '15 at 22:08

Arne Claassen · Answer 1 · 2015-07-30T22:51:53.570

6

In traditional OO programming methods are often made private so that they cannot be called by the outside and corrupt the state of the instance. Once your method is really a function without side-effects (as constructEmailMessage appears to be), there really isn't a reason to make it private.

As your purpose is to learn scala, I would encourage you to adopt a functional style operating on immutable data as much as possible, because it alleviates a lot of the reasons OO programming favors protected encapsulations.

edited Jul 30 '15 at 22:51

answered Jul 30 '15 at 22:10

Arne Claassen

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Agreed! The `Email` class sounds like the perfect thing to make into a `case class`! – childofsoong Jul 30 '15 at 22:50
Off the top of my head, 2 reasons for wanting to keep a function private: 1) you don't wan't to clutter the public API, 2) it is a helper function that you want to be able to freely refactor / rename without worrying about breaking client software. I'd pref Seth Tissue's recommendation and scope the method to `private[mypackage] def createMesssage(...` – Mark S Aug 01 '15 at 15:14
You can achieve both 1 & 2 by putting the public API in a trait, leaving your implementation to keep methods public (as long as they're stateless & idempotent). If you are worried about the API surface, package private still leaves the next maintainer of your package to accidentally use your private method. Personally, I prefer splitting public API and implementation as it is more explicit. Either works, tho – Arne Claassen Aug 01 '15 at 17:02

score 0 · Answer 2 · edited May 23 '17 at 12:21

You can use PowerMock library!

import org.powermock.reflect.Whitebox

val email = new Email("lalala@mail.com")
val expected = new Message(...)
val smtpHost = "127.0.0.1"

val actual = Whitebox.invokeMethod(email, "createMessage", smtpHost).asInstanceOf[Message]

assert(actual = expected)

This library also helpful for mocking private methods, but if you don't need its entire power for you tasks you can use reflection as mentioned in this post.

How to test non-public methods?

2 Answers2