[JS IR BE] Improve diagnostics in tests

js/js.tests/test/org/jetbrains/kotlin/js/test/BasicIrBoxTest.kt

@@ -115,7 +115,7 @@ abstract class BasicIrBoxTest(
         // TODO: should we do anything special for module systems?
         // TODO: return list of js from translateFiles and provide then to this function with other js files
         // TODO: cache runtime.js and don't cache kotlin.js for IR BE tests
-        super.runGeneratedCode(listOf(runtimeFile.path) + jsFiles, null, null, testFunction, expectedResult, false)
+        super.runGeneratedCode(listOf(runtimeFile.absolutePath) + jsFiles, null, null, testFunction, expectedResult, false)
     }
 }
 

js/js.translator/testData/_commonFiles/fail.kt

@@ -3,5 +3,9 @@ package kotlin
 // see StdLibTestBase.removeAdHocAssertions
 
 fun fail(message: String? = null): Nothing {
-    throw Exception(message)
+    // TODO: replace with next version when exception is supported properly
+    // throw Exception(message)
+
+    js("throw new Error(message)")
+    null!!
 }