[wpilib] Add Notifier test (#5070)

wpilibj/src/test/java/edu/wpi/first/wpilibj/NotifierTest.java

@@ -0,0 +1,63 @@
+// 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.jupiter.api.Assertions.assertEquals;
+
+import edu.wpi.first.hal.HAL;
+import edu.wpi.first.wpilibj.simulation.SimHooks;
+import java.util.concurrent.atomic.AtomicInteger;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.parallel.ResourceLock;
+
+/** Tests to see if the Notifier is working properly. */
+class NotifierTest {
+  @BeforeEach
+  void setup() {
+    HAL.initialize(500, 0);
+    SimHooks.pauseTiming();
+    SimHooks.restartTiming();
+  }
+
+  @AfterEach
+  void cleanup() {
+    SimHooks.resumeTiming();
+  }
+
+  @Test
+  @ResourceLock("timing")
+  void testStartPeriodicAndStop() {
+    AtomicInteger counter = new AtomicInteger();
+    Notifier notifier = new Notifier(counter::getAndIncrement);
+    notifier.startPeriodic(1.0);
+
+    SimHooks.stepTiming(10);
+
+    notifier.stop();
+    assertEquals(10, counter.get());
+
+    SimHooks.stepTiming(3.0);
+
+    assertEquals(10, counter.get());
+
+    notifier.close();
+  }
+
+  @Test
+  @ResourceLock("timing")
+  void testStartSingle() {
+    AtomicInteger counter = new AtomicInteger();
+    Notifier notifier = new Notifier(counter::getAndIncrement);
+    notifier.startSingle(1.0);
+
+    SimHooks.stepTiming(10.5);
+
+    assertEquals(1, counter.get());
+
+    notifier.close();
+  }
+}