feature: add a Scope trait to initialize variables in mutable specifications

Author: etorreborre

common/shared/src/main/scala/org/specs2/execute/Scope.scala

@@ -0,0 +1,17 @@
+package org.specs2.execute
+
+/** This trait can be used in mutable specifications to provide setup values. For example:
+  * ```scala
+  *    class MySpec extends mutable.Specification:
+  *       "e1" in new MyScope:
+  *         someValue === 1
+  *
+  *     trait MyScope extends Scope: val someValue: Int = 1
+  * ```
+  */
+trait Scope
+
+object Scope:
+  /** This Given transforms a Scope to a Result */
+  given scopeAsResult[S <: Scope]: AsResult[S] = new AsResult[S]:
+    def asResult(t: =>S): Result = AsResult.safely { Result.resultOrSuccess(t) }

core/jvm/src/test/scala/org/specs2/mutable/ScopeSpec.scala

@@ -0,0 +1,27 @@
+package org.specs2.mutable
+
+import org.specs2.specification.core.Env
+
+class ScopeSpec(env: Env) extends org.specs2.Specification:
+  def is = s2"""
+
+    A mutable specification can use the Scope trait to initialize values for each example $useScopeTrait
+  """
+
+  def useScopeTrait =
+    // make sure that the arguments show all examples
+    val arguments = org.specs2.main.Arguments("")
+    val result = org.specs2.runner.TextRunner.run(new ScopeSpecification)(env.setArguments(arguments)).output
+    (result must contain("+ This is an example which succeeds")) and
+      (result must contain("x This is an example which fails"))
+
+class ScopeSpecification extends org.specs2.mutable.Specification {
+  "This is an example which succeeds" in new SpecScope:
+    value === 1
+
+  "This is an example which fails" in new SpecScope:
+    value === 2
+}
+
+trait SpecScope extends org.specs2.execute.Scope:
+  val value: Int = 1