unit-tests: Add tests for test runner

backend.native/tests/testing/annotations.kt

@@ -1,3 +1,5 @@
+package kotlin.test.tests
+
 import kotlin.test.*
 import konan.test.*
 

backend.native/tests/testing/custom_main.kt

@@ -0,0 +1,14 @@
+package kotlin.test.tests
+
+import kotlin.test.*
+import konan.test.*
+
+@Test
+fun test() {
+    println("test")
+}
+
+fun main(args: Array<String>) {
+    println("Custom main")
+    TestRunner.run(args)
+}