Case class matchers

There is a special support for matching case classes:

  1. using shapeless to “project” a case class to another one containing less fields to match
  2. using a matcher macro

Both approaches are not incompatible, you can restrict the number of fields to match the remaining fields with more precise criteria.

Case class projection

You need to add the specs2-shapeless module to your project dependencies and add the org.specs2.shapeless.Projection._ import to your file.

Then you can “project” a type A on a “smaller” type B:

import org.specs2.shapeless.Projection._
case class User(id: Int, name: String, age: Int)
case class ExpectedUser(name: String, age: Int)

val u = User(123, "Martin", 58)

u.projectOn[ExpectedUser] must_== ExpectedUser("Martin", 58)

Matcher macro

You to add the specs2-matcher-extra module to your project dependencies and add the org.specs2.matcher.MatcherMacros trait to your specification.

Then, with the matchA matcher you can check the values of case class attributes:

// case class for a Cat
case class Cat(name: String = "", age: Int = 0, kitten: Seq[Cat] = Seq())
// a given cat
val cat = Cat(name = "Kitty", age = 6, kitten = Seq(Cat("Oreo", 1), Cat("Ella", 2)))

// this cat must be a Cat
cat must matchA[Cat]

// check the value of "name"
cat must matchA[Cat].name("Kitty")

// check the value of "age" using a matcher
def is[A](a: A) = be_==(a)
cat must matchA[Cat].age(is(6))

// check the value of "kitten" using a function returning a Result
cat must matchA[Cat].kitten((_:Seq[Cat]) must haveSize(2))

// matchers can be chained
cat must matchA[Cat]
  .kitten((_:Seq[Cat]) must haveSize(2))

And if you want to know more