Introduced the 'ensure' and 'ensureNotNull' functions

src/main/scala/in/rcard/raise4s/Builders.scala

@@ -1,4 +1,15 @@
 package in.rcard.raise4s
 
+/** Runs a computation `block` using [[Raise]], and return its outcome as [[Either]].
+  *  - [[Right]] represents success,
+  *  - [[Left]] represents logical failure.
+  *
+  * This function re-throws any exceptions thrown within the [[Raise]] block.
+  *
+  * @param block A computation that can raise errors of type `Error`
+  * @tparam A The type of the value returned by the computation
+  * @tparam Error The type of the logical error that can be raised by the computation
+  * @return An [[Either]] representing the outcome of the computation
+  */
 def either[A, Error](block: Raise[Error] ?=> () => A): Either[Error, A] =
   fold(block, error => Left(error), value => Right(value))

src/main/scala/in/rcard/raise4s/Raise.scala

@@ -2,7 +2,14 @@ package in.rcard.raise4s
 
 trait Raise[-Error]:
   def raise(e: Error): Nothing
-  
+
 infix type raises[R, Error] = Raise[Error] ?=> R
 
 def raise[Error](e: Error)(using raise: Raise[Error]): Nothing = raise.raise(e)
+
+def ensure[Error](condition: Boolean, raise: () => Error)(using r: Raise[Error]): Unit =
+  if !condition then r.raise(raise())
+
+def ensureNotNull[B, Error](value: B, raise: () => Error)(using r: Raise[Error]): B =
+  if value == null then r.raise(raise())
+  else value

src/test/scala/in/rcard/raise4s/RaiseSpec.scala

@@ -0,0 +1,12 @@
+package in.rcard.raise4s
+
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should.Matchers
+
+class RaiseSpec extends AnyFlatSpec with Matchers {
+
+  "ensureNotNull" should "return the value if it is not null" in {
+    // TODO: Implement the test
+    true should be(true)
+  }
+}