[wpilib] Add Notifier integration tests (#3480)

Closes #2610.

wpilibjIntegrationTests/src/main/java/edu/wpi/first/wpilibj/NotifierTest.java

@@ -0,0 +1,56 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+package edu.wpi.first.wpilibj;
+
+import static org.junit.Assert.assertEquals;
+
+import edu.wpi.first.wpilibj.test.AbstractComsSetup;
+import java.util.logging.Logger;
+import org.junit.Test;
+
+/** Tests to see if the Notifier is working properly. */
+public class NotifierTest extends AbstractComsSetup {
+  private static final Logger logger = Logger.getLogger(NotifierTest.class.getName());
+  private static int counter = 0;
+
+  @Override
+  protected Logger getClassLogger() {
+    return logger;
+  }
+
+  @Test
+  public void testStartPeriodicAndStop() {
+    counter = 0;
+    Notifier notifier = new Notifier(() -> ++counter);
+    notifier.startPeriodic(1.0);
+
+    Timer.delay(10.5);
+
+    notifier.stop();
+    assertEquals("Received " + counter + " notifications in 10.5 seconds\n", 10, counter);
+    System.out.println("Received " + counter + " notifications in 10.5 seconds");
+
+    Timer.delay(3.0);
+
+    assertEquals("Received " + (counter - 10) + " notifications in 3 seconds\n", 10, counter);
+    System.out.println("Received " + (counter - 10) + " notifications in 3 seconds");
+
+    notifier.close();
+  }
+
+  @Test
+  public void testStartSingle() {
+    counter = 0;
+    Notifier notifier = new Notifier(() -> ++counter);
+    notifier.startSingle(1.0);
+
+    Timer.delay(10.5);
+
+    assertEquals("Received " + counter + " notifications in 10.5 seconds\n", 1, counter);
+    System.out.println("Received " + counter + " notifications in 10.5 seconds");
+
+    notifier.close();
+  }
+}