Writing a Small DSL

In this section, we'll reimplement some FlatSpec ScalaTest DSLs in order to see how to implement DSLs in Scala.

First, we'll have a look at a simple way to model test cases in Scala using case classes. Then, we'll have a look at how to create a little DSL for creating those test cases.

Modeling Test Cases

Before we can create a DSL, we need to have something to create a DSL for. In our case, we want to create a DSL for specifying tests, so let's have a look at how we could model tests using case classes in Scala:

sealed trait TestResult
case class TestFailure(message: String) extends TestResult
case object TestSuccess extends TestResult

We'll create an algebraic data type that represents the result of running a test case. The result can either be a failure that contains a message regarding the failure, or a TestSuccess that simply indicates that the test passed:

case class TestCase(description: TestDescription, run: () => TestResult)
case class TestDescription(name...