Simplify largeMessage test

Further, reduce some code duplication.

Author: gzm0

js-envs-test-kit/src/main/scala/org/scalajs/jsenv/test/ComTests.scala

@@ -79,57 +79,26 @@ private[test] class ComTests(config: JSEnvSuiteConfig) {
     }
   }
 
-  @Test
-  def largeMessageTest: Unit = {
-    // 1KB data
-    val baseMsg = new String(Array.tabulate(512)(_.toChar))
-    val baseLen = baseMsg.length
-
-    // Max message size: 1KB * 2^(2*iters+1) = 1MB
-    val iters = 4
-
-    val run = kit.start("""
-      scalajsCom.init(function(msg) {
-        scalajsCom.send(msg + msg);
-      });
-    """, RunConfig())
+  private def replyTest(msg: String) = {
+    val run = kit.start("scalajsCom.init(scalajsCom.send);", RunConfig())
 
     try {
-      run.run.send(baseMsg)
-
-      def resultFactor(iters: Int) = Math.pow(2, 2 * iters + 1).toInt
-
-      for (i <- 0 until iters) {
-        val reply = run.waitNextMessage()
-
-        val factor = resultFactor(i)
-
-        assertEquals(baseLen * factor, reply.length)
-
-        for (j <- 0 until factor)
-          assertEquals(baseMsg, reply.substring(j * baseLen, (j + 1) * baseLen))
-
-        run.run.send(reply + reply)
-      }
-
-      val lastLen = run.waitNextMessage().length
-      assertEquals(baseLen * resultFactor(iters), lastLen)
+      run.run.send(msg)
+      assertEquals(msg, run.waitNextMessage())
     } finally {
       run.closeAndWait()
     }
   }
 
   @Test
-  def highCharTest: Unit = { // #1536
-    val run = kit.start("scalajsCom.init(scalajsCom.send);", RunConfig())
+  def largeMessageTest: Unit = {
+    // 1MB data
+    replyTest(new String(Array.tabulate(1024 * 1024)(_.toChar)))
+  }
 
-    try {
-      val msg = "\uC421\u8F10\u0112\uFF32"
-      run.run.send(msg)
-      assertEquals(msg, run.waitNextMessage())
-    } finally {
-      run.closeAndWait()
-    }
+  @Test
+  def highCharTest: Unit = { // #1536
+    replyTest("\uC421\u8F10\u0112\uFF32")
   }
 
   @Test