[SPARK-26082][MESOS][FOLLOWUP] Add UT on fetcher cache option on MesosClusterScheduler

## What changes were proposed in this pull request?

This patch adds UT on testing SPARK-26082 to avoid regression. While apache#23743 reduces the possibility to make a similar mistake, the needed lines of code for adding tests are not that huge, so I guess it might be worth to add them.

## How was this patch tested?

Newly added UTs. Test "supports setting fetcher cache" fails when apache#23743 is not applied and succeeds when apache#23743 is applied.

Closes apache#23744 from HeartSaVioR/SPARK-26082-add-unit-test.

Authored-by: Jungtaek Lim (HeartSaVioR) <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>
(cherry picked from commit b4e1d14)
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: HeartSaVioR

resource-managers/mesos/src/test/scala/org/apache/spark/scheduler/cluster/mesos/MesosClusterSchedulerSuite.scala

@@ -254,6 +254,54 @@ class MesosClusterSchedulerSuite extends SparkFunSuite with LocalSparkContext wi
     assert(networkInfos.get(0).getLabels.getLabels(1).getValue == "val2")
   }
 
+  test("supports setting fetcher cache") {
+    setScheduler(Map("spark.mesos.fetcherCache.enable" -> "true"))
+
+    val mem = 1000
+    val cpu = 1
+
+    val response = scheduler.submitDriver(
+      new MesosDriverDescription("d1", "jar", mem, cpu, true,
+        command,
+        Map("spark.mesos.executor.home" -> "test",
+          "spark.app.name" -> "test"),
+        "s1",
+        new Date()))
+
+    assert(response.success)
+
+    val offer = Utils.createOffer("o1", "s1", mem, cpu)
+    scheduler.resourceOffers(driver, List(offer).asJava)
+
+    val launchedTasks = Utils.verifyTaskLaunched(driver, "o1")
+    val uris = launchedTasks.head.getCommand.getUrisList
+    assert(uris.stream().allMatch(_.getCache))
+  }
+
+  test("supports disabling fetcher cache") {
+    setScheduler(Map("spark.mesos.fetcherCache.enable" -> "false"))
+
+    val mem = 1000
+    val cpu = 1
+
+    val response = scheduler.submitDriver(
+      new MesosDriverDescription("d1", "jar", mem, cpu, true,
+        command,
+        Map("spark.mesos.executor.home" -> "test",
+          "spark.app.name" -> "test"),
+        "s1",
+        new Date()))
+
+    assert(response.success)
+
+    val offer = Utils.createOffer("o1", "s1", mem, cpu)
+    scheduler.resourceOffers(driver, List(offer).asJava)
+
+    val launchedTasks = Utils.verifyTaskLaunched(driver, "o1")
+    val uris = launchedTasks.head.getCommand.getUrisList
+    assert(uris.stream().allMatch(!_.getCache))
+  }
+
   test("accept/decline offers with driver constraints") {
     setScheduler()