Unit testing API: better mapping on JUnit, proper formatting assertion details when message is not specified

#KT-8929 Fixed
Sensible default message for assertion methods.
#KT-8314 Fixed
Provide assertFailsWith also with KClass and reified type argument.

libraries/kunit/src/main/kotlin/junit/JUnit.kt

@@ -4,27 +4,23 @@ import kotlin.test.Asserter
 import org.junit.Assert
 
 class JUnitAsserter : Asserter {
-    override fun assertEquals(message : String, expected : Any?, actual : Any?) {
+    override fun assertEquals(message : String?, expected : Any?, actual : Any?) {
         Assert.assertEquals(message, expected, actual)
     }
 
-    override fun assertNotEquals(message : String, illegal : Any?, actual : Any?) {
+    override fun assertNotEquals(message : String?, illegal : Any?, actual : Any?) {
         Assert.assertNotEquals(message, illegal, actual)
     }
 
-    override fun assertNotNull(message : String, actual : Any?) {
+    override fun assertNotNull(message : String?, actual : Any?) {
         Assert.assertNotNull(message, actual)
     }
 
-    override fun assertNull(message : String, actual : Any?) {
+    override fun assertNull(message : String?, actual : Any?) {
         Assert.assertNull(message, actual)
     }
 
-    override fun assertTrue(message : String, actual : Boolean) {
-        Assert.assertTrue(message, actual)
-    }
-
-    override fun fail(message : String) {
+    override fun fail(message : String?) {
         Assert.fail(message)
     }
 }