Add failing test: Fix Seq/Array atOrElse throwing IndexOutOfBoundsException for missing indices

Author: adamw

quicklens/src/test/scala/com/softwaremill/quicklens/ModifySeqAtOrElseTest.scala

@@ -0,0 +1,23 @@
+package com.softwaremill.quicklens
+
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should.Matchers
+
+class ModifySeqAtOrElseTest extends AnyFlatSpec with Matchers {
+
+  case class Item(name: String)
+
+  it should "modify an existing element using atOrElse" in {
+    val items = List(Item("a"), Item("b"))
+    modify(items)(_.atOrElse(1, Item("default")).name).using(_.toUpperCase) should be(
+      List(Item("a"), Item("B"))
+    )
+  }
+
+  it should "use the default for a missing index instead of throwing" in {
+    val items = List(Item("a"), Item("b"))
+    modify(items)(_.atOrElse(5, Item("default")).name).using(_.toUpperCase) should be(
+      List(Item("a"), Item("b"), Item("DEFAULT"))
+    )
+  }
+}