[Tests] Test samples from KEEP

compiler/testData/codegen/box/extensionFunctions/contextReceivers/fromKEEP/monoidSum.kt

@@ -0,0 +1,31 @@
+// TARGET_BACKEND: JVM_IR
+// IGNORE_BACKEND_FIR: JVM_IR
+// WITH_RUNTIME
+
+interface Semigroup<T> {
+    infix fun T.combine(other: T): T
+}
+
+interface Monoid<T> : Semigroup<T> {
+    val unit: T
+}
+object IntMonoid : Monoid<Int> {
+    override fun Int.combine(other: Int): Int = this + other
+    override val unit: Int = 0
+}
+object StringMonoid : Monoid<String> {
+    override fun String.combine(other: String): String = this + other
+    override val unit: String = ""
+}
+
+context(Monoid<T>)
+fun <T> List<T>.sum(): T = fold(unit) { acc, e -> acc.combine(e) }
+
+fun box(): String {
+    with(IntMonoid) {
+        listOf(1, 2, 3).sum()
+    }
+    return with(StringMonoid) {
+        listOf("O", "K").sum()
+    }
+}