Introduce 'fail' method to throw AssertionError with cause

#KT-37804

libraries/kotlin.test/js/src/main/kotlin/kotlin/test/DefaultJsAsserter.kt

@@ -57,7 +57,7 @@ internal object DefaultJsAsserter : Asserter {
 
     override fun assertTrue(lazyMessage: () -> String?, actual: Boolean) {
         if (!actual) {
-            failWithMessage(lazyMessage)
+            failWithMessage(lazyMessage, null)
         } else {
             invokeHook(true, lazyMessage)
         }
@@ -68,16 +68,18 @@ internal object DefaultJsAsserter : Asserter {
     }
 
     override fun fail(message: String?): Nothing {
-        failWithMessage { message }
+        fail(message, null)
     }
 
-    private fun failWithMessage(lazyMessage: () -> String?): Nothing {
+    @SinceKotlin("1.4")
+    override fun fail(message: String?, cause: Throwable?): Nothing {
+        failWithMessage({ message }, cause)
+    }
+
+    private inline fun failWithMessage(lazyMessage: () -> String?, cause: Throwable?): Nothing {
         val message = lazyMessage()
         invokeHook(false) { message }
-        if (message == null)
-            throw AssertionError()
-        else
-            throw AssertionError(message)
+        throw AssertionErrorWithCause(message, cause)
     }
 
     private fun invokeHook(result: Boolean, lazyMessage: () -> String?) {

libraries/kotlin.test/js/src/main/kotlin/kotlin/test/JsImpl.kt

@@ -17,6 +17,11 @@ actual fun todo(block: () -> Unit) {
     println("TODO at " + block)
 }
 
+/** Platform-specific construction of AssertionError with cause */
+@Suppress("NOTHING_TO_INLINE")
+internal actual inline fun AssertionErrorWithCause(message: String?, cause: Throwable?): AssertionError =
+    AssertionError(message, cause)
+
 
 @PublishedApi
 internal actual fun <T : Throwable> checkResultIsFailure(exceptionClass: KClass<T>, message: String?, blockResult: Result<Unit>): T {