[Gradle, JS] Add configuration cache test for Karma test task

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kotlin-js-browser-project/app/build.gradle.kts

@@ -6,6 +6,7 @@ dependencies {
     implementation(kotlin("stdlib-js"))
     implementation(project(":lib"))
     implementation(npm(projectDir.resolve("src/main/css")))
+    testImplementation(kotlin("test-js"))
 }
 
 kotlin {
@@ -14,6 +15,13 @@ kotlin {
             webpackTask {
                 cssSupport.enabled = true
             }
+            testTask {
+                useKarma {
+                    useChromeHeadless()
+                }
+                enabled = false // Task is disabled because it requires browser to be installed. That may be a problem on CI.
+                                // Disabled but configured task allows us to check at least a part of configuration cache correctness.
+            }
         }
         binaries.executable()
 

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/kotlin-js-browser-project/app/src/test/kotlin/AppTests.kt

@@ -0,0 +1,16 @@
+/*
+ * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package com.example
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class AppTests {
+    @Test
+    fun testSheldon() {
+        assertEquals(73, sheldon())
+    }
+}