DefaultAsserter object. Add function to replace constructor invoke.

libraries/kotlin.test/common/src/main/kotlin/kotlin/test/DefaultAsserter.kt

@@ -8,8 +8,7 @@ package kotlin.test
 /**
  * Default [Asserter] implementation to avoid dependency on JUnit or TestNG.
  */
-// TODO: make object in 1.2
+object DefaultAsserter : Asserter {
-class DefaultAsserter : Asserter {
     override fun fail(message: String?): Nothing {
         if (message == null)
             throw AssertionError()
@@ -17,3 +16,9 @@ class DefaultAsserter : Asserter {
             throw AssertionError(message)
     }
 }
+
+@Deprecated("DefaultAsserter is an object now, constructor call is not required anymore",
+        ReplaceWith("DefaultAsserter", "kotlin.test.DefaultAsserter"))
+@kotlin.js.JsName("DefaultAsserterConstructor")
+@Suppress("FunctionName")
+fun DefaultAsserter(): DefaultAsserter = DefaultAsserter

libraries/kotlin.test/common/src/main/kotlin/kotlin/test/Utils.kt

@@ -9,9 +9,4 @@ internal fun messagePrefix(message: String?) = if (message == null) "" else "$me
 internal expect fun lookupAsserter(): Asserter
 
 @PublishedApi // required to get stable name as it's called from box tests
-internal fun overrideAsserter(value: Asserter?): Asserter? {
+internal fun overrideAsserter(value: Asserter?): Asserter? = _asserter.also { _asserter = value }
-    // TODO: Replace with return _asserter.also { _asserter = value } after KT-17540 is fixed
-    val previous = _asserter
-    _asserter = value
-    return previous
-}

libraries/kotlin.test/common/src/test/kotlin/kotlin/test/tests/BasicAssertionsTest.kt

@@ -199,7 +199,7 @@ private fun checkFailedAssertion(assertion: () -> Unit) {
 
 @Suppress("INVISIBLE_MEMBER")
 private fun withDefaultAsserter(block: () -> Unit) {
-    val current = overrideAsserter(DefaultAsserter())
+    val current = overrideAsserter(DefaultAsserter)
     try {
         block()
     } finally {

libraries/kotlin.test/jvm/src/main/kotlin/AsserterLookup.kt

@@ -9,12 +9,10 @@ import java.util.ServiceLoader
 
 private val contributors = ServiceLoader.load(AsserterContributor::class.java).toList()
 
-private val defaultAsserter = DefaultAsserter()
-
 internal actual fun lookupAsserter(): Asserter {
     for (contributor in contributors) {
         val asserter = contributor.contribute()
         if (asserter != null) return asserter
     }
-    return defaultAsserter
+    return DefaultAsserter
 }