[K/N][Tests] Adjust moved codegen tests to new infra

^KT-61259

native/native.tests/testData/codegen/boxing/boxing6.kt

@@ -3,21 +3,24 @@
  * that can be found in the LICENSE file.
  */
 
-package codegen.boxing.boxing6
-
 import kotlin.test.*
 
-fun printInt(x: Int) = println(x)
+val sb = StringBuilder()
+
+fun printInt(x: Int) = sb.appendLine(x)
 
 fun foo(arg: Any) {
     printInt(arg as? Int ?: 16)
 }
 
-@Test fun runTest() {
+fun box(): String {
     foo(42)
     foo("Hello")
     val nonConstInt = 42
     val nonConstString = "Hello"
     foo(nonConstInt)
     foo(nonConstString)
+
+    assertEquals("42\n16\n42\n16\n", sb.toString())
+    return "OK"
 }