[JS IR] Support IR dump in JS tests

compiler/test-infrastructure/ReadMe.md

@@ -337,6 +337,31 @@ abstract class MyAnotherAbstractTestRunner : MyAbstractTestRunner() {
 }
 ```
 
+# Debugging tests (JS and WASM only):
+
+Kotlin/JS and Kotlin/WASM tests support the following system properties to make debugging them more convenient:
+- `kotlin.js.debugMode` for setting a debug mode for Kotlin/JS tests
+- `kotlin.wasm.debugMode` for setting a debug mode for Kotlin/WASM tests
+- `org.jetbrains.kotlin.compiler.ir.dump.strategy` for the IR dump strategy to use. Set it to `"KotlinLike"`
+   if you want the IR dump to be more human-readable.
+
+Note that to pass a system property from gradle task invocation, its name should be prefixed with `fd.`.
+For example, to debug Kotlin/JS tests, run:
+
+```
+./gradlew :js:js.tests:jsIrTest -Pfd.kotlin.js.debugMode=2
+```
+
+To debug WASM tests, run:
+```
+./gradlew :js:js.tests:wasmTest -Pfd.kotlin.wasm.debugMode=2
+```
+
+Values of the debug mode: `0` (or `false`), `1` (or `true`), `2`.
+
+Debug mode `2` will ensure that IR is dumped to a file after each lowering phase.
+The IR dumps will appear next to the generated `.js` or `.wat` file.
+
 # Code style
 
 Please keep your abstract test runners as simple as possible. Ideally each abstract test runner should contain **only** test configuration with DSL and nothing else. All services implementations should be declared in separate files. 

compiler/tests-common/tests/org/jetbrains/kotlin/test/DebugMode.kt

@@ -0,0 +1,30 @@
+/*
+ * 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 org.jetbrains.kotlin.test
+
+/**
+ * Represents a mode fore debugging tests. Depending on what is tested, can represent different things.
+ * For example, in JS IR and WASM tests the selected mode will determine if the test output should include IR dumps.
+ */
+enum class DebugMode {
+    NONE,
+    DEBUG,
+    SUPER_DEBUG;
+
+    companion object {
+
+        /**
+         * Obtains a [DebugMode] from the system property with the given [key].
+         * If the property is not defined, returns [NONE].
+         */
+        fun fromSystemProperty(key: String): DebugMode = when (System.getProperty(key)) {
+            "2", "super_debug" -> SUPER_DEBUG
+            "1", "true", "debug" -> DEBUG
+            "0", "false", "", null -> NONE
+            else -> NONE
+        }
+    }
+}