Custom types support with Repr

Snapshot4s serializes the runtime values to it's source code representation. It does that by utilizing the Repr typeclass. The library is able to automatically derive the implementation for primitive types, collections from standard library along with Option and Either. As for now it's implemented using PPrint but that might change in future.

In case the Repr instance is missing for your type MyType, you'll see a message like this:

Compiler error

Could not find implicit instance for Repr[MyType]. This usually means that MyType or it's component is not an ADT or primitive type. In that case provide your own given instance of Repr[MyType]. Repr.fromPprint can be used to generate it.

If you want to assert snapshot against a type MyType, for which the library doesn't derive the implementation, you can implement your own instance of Repr[MyType]. Make sure to mark to expose it in implicit scope (with implicit val in Scala 2 or given in Scala 3).

Defining your own Repr

There are two ways of implementing Repr. If your type MyType serializes to source code properly with PPrint, you can simply do given Repr[MyType] = Repr.fromPprint[MyType]. While convenient, this method does not always produce satisfying results. For example types that come from Java will not serialize nicely. In that case you can define Repr as follows:

import java.util.UUID
import snapshot4s.Repr

case class User(name: String, id: UUID)
def getUsers(): List[User] = ???

// here we define custom Repr implementation for UUID, using Single Abstract Method syntax
given Repr[UUID] = (uuid: UUID) => s"""UUID.fromString("${uuid.toString}")"""

test("should get users") {
  val users = getUsers()
  assertInlineSnapshot(
    users,
    List(
      User(name = "admin", id = UUID.fromString("6e09d8b0-b7c9-4cbe-ac96-8c27c36cd2c6")),
      User(name = "alice", id = UUID.fromString("ff8b8542-183f-4eff-acb0-6436936ccc31")),
      User(name = "bob", id = UUID.fromString("30046607-623d-4934-b8f6-4002ef4ff588"))
    )
  )
  //                           ☝️ notice how UUID representation follows our Repr implementation
}