Make assertions worker-friendly. (#2152)

backend.native/tests/runtime/workers/worker0.kt

@@ -12,7 +12,10 @@ import kotlin.native.concurrent.*
 @Test fun runTest() {
     val worker = Worker.start()
     val future = worker.execute(TransferMode.SAFE, { "Input" }) {
-        input -> input + " processed"
+        input ->
+        assertEquals(1, 1)
+        assertFailsWith<AssertionError> { assertEquals(1, 2) }
+        input + " processed"
     }
     future.consume {
         result -> println("Got $result")

backend.native/tests/testing/assertions.kt

@@ -172,11 +172,5 @@ private fun checkFailedAssertion(assertion: () -> Unit) {
 
 @Suppress("INVISIBLE_MEMBER")
 private fun withDefaultAsserter(block: () -> Unit) {
-    val current = overrideAsserter(DefaultAsserter)
-    try {
-        block()
-    }
-    finally {
-        overrideAsserter(current)
-    }
+    block()
 }

runtime/src/main/kotlin/kotlin/test/Assertions.kt

@@ -18,10 +18,7 @@ import kotlin.reflect.KClass
  * Current adapter providing assertion implementations
  */
 private val asserter: Asserter
-    get() = _asserter ?: lookupAsserter()
-
-/** Used to override current asserter internally */
-internal var _asserter: Asserter? = null
+    get() = DefaultAsserter
 
 /** Asserts that the given [block] returns `true`. */
 public fun assertTrue(message: String? = null, block: () -> Boolean): Unit = assertTrue(block(), message)

runtime/src/main/kotlin/kotlin/test/Utils.kt

@@ -6,9 +6,4 @@
 package kotlin.test
 
 @PublishedApi
-internal fun messagePrefix(message: String?) = if (message == null) "" else "$message. "
-
-internal fun lookupAsserter(): Asserter = DefaultAsserter
-
-@PublishedApi // required to get stable name as it's called from box tests
-internal fun overrideAsserter(value: Asserter?): Asserter? = _asserter.also { _asserter = value }
+internal fun messagePrefix(message: String?) = if (message == null) "" else "$message. "