CODEWITHSUNDEEP
scalatestingmockingmockitoscalatest
Traveling Tech Guy
Traveling Tech Guy

Reputation: 27849

How to use mocks in Scala to mock a singleton object

I recently started programming in Scala. I have a project with a hierarchy of classes that call each other. Eventually, they last one calls a singleton DAL (Data Access Layer) object that calls a stored procedure in MySQL.

I have a DAL object with the following signature:

def callStoredProcedure(procName: String, params: Array[String]): Boolean

I'd like to write a test that calls a function of the top level class, and checks out what procName was passed to the function.

How do I go about creating a mock for the DAL object? How can I inject it into the process pipeline, or is there a better/recommended way to replace the singleton with a mock that just returns the procedure name rather than calling it?

We're currently using Mockito, but I'm open to anything.

Upvotes: 0

Views: 1711

Answers (2)

Joan
Joan

Reputation: 4320

You can do:

class Foo(dal: DAL)

val testMe = new Foo(dal = mock[DAL.type])

Cheers

Upvotes: 0

Dima
Dima

Reputation: 40508

Don't use singletons directly, that's not a good idea. You know why? Because you can't mock them for unit testing, duh. Make it a parameter to your class instead:

trait DAL {
  def callStoredProcedure(procName: String, params: Array[String]): Boolean       
}

object DALImpl extends DAL {
    def callStoredProcedure(procName: String, params: Array[String]): Boolean = doStuff
}

class Foo(dal: DAL = DALImpl) 

val testMe = new Foo(mock[DAL])

or 

class Foo {
    def dal: DAL = DALImpl
}

val testMe = new Foo {
  override def dal = mock[DAL]
}

Upvotes: 3

Related Questions