Select the asserter based on test framework presence in classpath

Simplify asserter lookup: enumerate all AsserterContributors when
the file class with lookupAsserter function is initialized.

It's assumed that AsserterContributor initialization should be fast.

#KT-21154 Fixed

libraries/kotlin.test/testng/src/main/kotlin/TestNGSupport.kt

@@ -8,20 +8,25 @@ package kotlin.test.testng
 import org.testng.*
 import kotlin.test.*
 
+/**
+ * Provides [TestNGAsserter] if `org.testng.Assert` is found in the classpath.
+ */
 class TestNGContributor : AsserterContributor {
     override fun contribute(): Asserter? {
-        for (stackFrame in currentStackTrace()) {
-            val className = stackFrame.className
+        return if (hasTestNGInClassPath) TestNGAsserter else null
+    }
 
-            if (className.startsWith("org.testng.") || className.startsWith("testng.")) {
-                return TestNGAsserter
-            }
-        }
-
-        return null
+    private val hasTestNGInClassPath = try {
+        Class.forName("org.testng.Assert")
+        true
+    } catch (_: ClassNotFoundException) {
+        false
     }
 }
 
+/**
+ * Implements `kotlin.test` assertions by delegating them to `org.testng.Assert` class.
+ */
 object TestNGAsserter : Asserter {
     override fun assertEquals(message: String?, expected: Any?, actual: Any?) {
         Assert.assertEquals(expected, actual, message)

libraries/kotlin.test/testng/src/test/kotlin/TestNGContributorTest.kt

@@ -1,25 +1,27 @@
 package kotlin.test.testng.tests
 
-import org.testng.annotations.*
-import org.testng.*
+import org.testng.Assert
+import kotlin.test.*
 import java.util.concurrent.*
+import kotlin.test.testng.TestNGAsserter
 
 class TestNGContributorTest {
 
     @Test
     fun smokeTest() {
-        Assert.assertEquals("TestNGAsserter", kotlin.test.asserter.javaClass.simpleName)
+        assertSame(TestNGAsserter, asserter)
+        Assert.assertEquals(TestNGAsserter::class.java.simpleName, kotlin.test.asserter.javaClass.simpleName)
     }
 
     @Test
-    fun `should fail to contribute if it was run outside of testng`() {
+    fun parallelThreadGetsTheSameAsserter() {
         val q = ArrayBlockingQueue<Any>(1)
 
         Thread {
-            q.put(kotlin.test.asserter)
+            q.put(asserter)
         }.start()
 
-        Assert.assertEquals("DefaultAsserter", q.take().javaClass.simpleName)
+        assertSame(asserter, q.take())
     }
 
-}
+}