Target test for extension copy (softwaremill#234)

quicklens/src/test/scala-3/com/softwaremill/quicklens/test/ExtensionCopyTest.scala

@@ -0,0 +1,50 @@
+package com.softwaremill.quicklens
+package test
+
+import org.scalatest.flatspec.AnyFlatSpec
+import org.scalatest.matchers.should.Matchers
+
+object ExtensionCopyTest {
+  case class V(x: Double, y: Double)
+
+  opaque type Vec = V
+
+  object Vec {
+    def apply(x: Double, y: Double): Vec = V(x, y)
+  }
+
+  extension (v: Vec) {
+    def x: Double = v.x
+    def y: Double = v.y
+    def copy(x: Double = v.x, y: Double = v.y): Vec = V(x, y)
+  }
+}
+
+class ExtensionCopyTest extends AnyFlatSpec with Matchers {
+  it should "modify a class with an extension copy method" in {
+    case class V(x: Double, y: Double)
+
+    class Vec(val v: V)
+
+    object Vec {
+      def apply(x: Double, y: Double): Vec = new Vec(V(x, y))
+    }
+
+    extension (v: Vec) {
+      def x: Double = v.v.x
+      def y: Double = v.v.y
+      def copy(x: Double = v.x, y: Double = v.y): Vec = new Vec(V(x, y))
+    }
+    val a = Vec(1, 2)
+    val b = a.modify(_.x).using(_ + 1)
+    println(b)
+  }
+
+  it should "modify an opaque type with an extension copy method" in {
+    import ExtensionCopyTest.*
+
+    val a = Vec(1, 2)
+    val b = a.modify(_.x).using(_ + 1)
+    println(b)
+  }
+}