Added sample code for find, filter and collect

build.sbt

@@ -430,6 +430,10 @@ lazy val scala3_lang_2 = (project in file("scala3-lang-2")).settings(
   libraryDependencies ++= scalaTestDeps
 )
 
+lazy val scala3_lang_3 = (project in file("scala3-lang-3")).settings(
+  libraryDependencies ++= scalaTestDeps
+)
+
 lazy val cats_effects = (project in file("cats-effects"))
   .settings(
     name := "cats-effects",

scala3-lang-3/src/test/scala/com/baeldung/scala/filters/FindFilterCollector.scala

@@ -0,0 +1,112 @@
+package com.baeldung.scala.filters
+
+import org.scalatest.matchers.should.Matchers
+import org.scalatest.wordspec.AnyWordSpec
+
+import scala.collection.SortedSet
+
+class FindFilterCollector extends AnyWordSpec with Matchers {
+  "find method" should {
+    "select one element from a collection using find method" in {
+      val numbers = List(1, 2, 3, 4, 5, 6)
+      numbers.find(_ % 2 == 0) shouldBe Some(2)
+    }
+
+    "return None if no value matches with the predicate" in {
+      val numbers = List(1, 2, 3, 4, 5, 6)
+      numbers.find(_ > 9) shouldBe None
+    }
+
+    "find the first match based on the ordering of the collection type" in {
+      val numbers = SortedSet(9, 8, 6, 2, 4)
+      numbers.find(_ % 2 == 0) shouldBe Some(2)
+    }
+
+    "find the last match on linear collection (not available on sets)" in {
+      val numbers = List(1, 2, 3, 4, 5, 6)
+      numbers.findLast(_ % 2 == 0) shouldBe Some(6)
+    }
+  }
+
+  "filter method" should {
+    "return all elements matching the condition" in {
+      val numbers = List(1, 2, 3, 4, 5, 6)
+      val oddNumbers = numbers.filter(_ % 2 == 1)
+      oddNumbers shouldBe List(1, 3, 5)
+    }
+
+    "return empty collection if nothing matches" in {
+      val numbers = List(2, 4, 6, 8)
+      val oddNumbers = numbers.filter(_ % 2 == 1)
+      oddNumbers shouldBe empty
+    }
+
+    "use a complex predicate" in {
+      val numbers = List(1, 2, 3, 4, 5, 6)
+      val oddAndNotMulOf3or5 =
+        numbers.filter(n => (n % 2 == 1 && n % 3 != 0 && n % 5 != 0))
+      oddAndNotMulOf3or5 shouldBe List(1)
+    }
+
+    "use a function as predicate" in {
+      def isOddAndNotMulOf3or5(n: Int) =
+        n % 2 == 1 && n % 3 != 0 && n % 5 != 0
+      val numbers = List(1, 2, 3, 4, 5, 6)
+      val oddAndNotMulOf3or5 =
+        numbers.filter(isOddAndNotMulOf3or5)
+      oddAndNotMulOf3or5 shouldBe List(1)
+    }
+  }
+
+  "filterNot method" should {
+    "apply the negate of the predicate" in {
+      val numbers = List(1, 2, 3, 4, 5, 6)
+      val nonOdd = numbers.filterNot(_ % 2 == 1)
+      val even = numbers.filter(_ % 2 != 1)
+      nonOdd shouldBe even
+    }
+  }
+
+  "collect method" should {
+    "collect the elements matching the condition" in {
+      val numbers = List(1, 2, 3, 4, 5, 6)
+      val even = numbers.collect {
+        case n if n % 2 == 0 => n
+      }
+      even shouldBe List(2, 4, 6)
+    }
+
+    "collect the elements matching the condition and square it" in {
+      val numbers = List(1, 2, 3, 4, 5, 6)
+      val evenSquared = numbers.collect {
+        case n if n % 2 == 0 => n * n
+      }
+      evenSquared shouldBe List(4, 16, 36)
+    }
+
+    "collect and filter map be equivalent" in {
+      val numbers = List(1, 2, 3, 4, 5, 6)
+      val evenSquared = numbers.filter(_ % 2 == 0).map(n => n * n)
+      evenSquared shouldBe List(4, 16, 36)
+    }
+
+    "collectFirst" should {
+      "return the first element matching the partial function" in {
+        val numbers = List(1, 2, 3, 4, 5, 6)
+        val firstEven = numbers.collectFirst {
+          case n if n % 2 == 0 => n
+        }
+        firstEven shouldBe Some(2)
+      }
+
+      "return the first element matching the partial function in the same order of collection" in {
+        val numbers = SortedSet(6, 5, 4, 3, 2, 1)
+        val firstEven = numbers.collectFirst {
+          case n if n % 2 == 0 => n
+        }
+        firstEven shouldBe Some(2)
+      }
+    }
+  }
+
+}