Provide test coverage for NonEmptyList (#3135)

* [feature/add_non_empty_list_test] Add Method Tests

- lastOrNull
- extract

* add nonemptylist test (operator plus function)

* add coflatmap test

* add foldLeft test

* fix lint

* fix foldLeft unit test logic

---------

Co-authored-by: Alejandro Serrano <[email protected]>

Author: l2hyunwoo

arrow-libs/core/arrow-core/src/commonTest/kotlin/arrow/core/NonEmptyListTest.kt

@@ -12,10 +12,7 @@ import io.kotest.matchers.booleans.shouldBeTrue
 import io.kotest.matchers.nulls.shouldNotBeNull
 import io.kotest.matchers.shouldBe
 import io.kotest.property.Arb
-import io.kotest.property.arbitrary.boolean
-import io.kotest.property.arbitrary.int
-import io.kotest.property.arbitrary.negativeInt
-import io.kotest.property.arbitrary.pair
+import io.kotest.property.arbitrary.*
 import io.kotest.property.checkAll
 import kotlin.math.max
 import kotlin.math.min
@@ -445,4 +442,56 @@ class NonEmptyListTest : StringSpec({
         }
       }
     }
+
+    "lastOrNull" {
+      checkAll(
+        Arb.nonEmptyList(Arb.int())
+      ) { a ->
+        val result = a.lastOrNull()
+        val expected = a.last()
+        result shouldBe expected
+      }
+    }
+
+    "extract" {
+      checkAll(
+        Arb.nonEmptyList(Arb.int())
+      ) { a ->
+        val result = a.extract()
+        val expected = a.head
+        result shouldBe expected
+      }
+    }
+
+    "plus" {
+      checkAll(
+        Arb.nonEmptyList(Arb.int()),
+        Arb.int()
+      ) { a, b ->
+        val result = a + b
+        val expected = a.all + b
+        result shouldBe expected
+      }
+    }
+
+    "coflatMap should retain the same length as the original list" {
+      checkAll(
+        Arb.nonEmptyList(Arb.int())
+      ) { a ->
+        val result = a.coflatMap { it.all }
+        val expected = a.all
+        result.size shouldBe expected.size
+      }
+    }
+
+    "foldLeft should sum up correctly for addition" {
+      checkAll(
+        Arb.nonEmptyList(Arb.int()),
+        Arb.int()
+      ) { list, initial ->
+        val result = list.foldLeft(initial) { acc, i -> acc + i }
+        val expected = initial + list.all.sum()
+        result shouldBe expected
+      }
+    }
 })