Fix and unit test TimedTaskManager (#91)

Adds TimedTaskManager unit test and switches back to standard executor instead of the custom subclass.

photon-server/src/test/java/org/photonvision/common/util/TimedTaskManagerTest.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright (C) 2020 Photon Vision.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package org.photonvision.common.util;
+
+import java.util.concurrent.atomic.AtomicInteger;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class TimedTaskManagerTest {
+
+    @Test
+    public void atomicIntegerIncrementTest() throws InterruptedException {
+        AtomicInteger i = new AtomicInteger();
+        TimedTaskManager.getInstance().addTask("TaskManagerTest", i::getAndIncrement, 2);
+        Thread.sleep(400);
+        Assertions.assertEquals(200, i.get(), 5);
+    }
+}