[examples] AddressableLED: Add unit test (#4779)

wpilibjExamples/src/test/java/edu/wpi/first/wpilibj/examples/addressableled/RainbowTest.java

@@ -0,0 +1,54 @@
+// 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.examples.addressableled;
+
+import static org.junit.jupiter.api.Assertions.assertAll;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import edu.wpi.first.hal.HAL;
+import edu.wpi.first.wpilibj.simulation.AddressableLEDSim;
+import edu.wpi.first.wpilibj.util.Color;
+import edu.wpi.first.wpilibj.util.Color8Bit;
+import org.junit.jupiter.api.Test;
+
+class RainbowTest {
+  @Test
+  void rainbowPatternTest() {
+    HAL.initialize(500, 0);
+    try (var robot = new Robot()) {
+      robot.robotInit();
+      AddressableLEDSim ledSim = AddressableLEDSim.createForChannel(9);
+      assertTrue(ledSim.getRunning());
+      assertEquals(60, ledSim.getLength());
+
+      var rainbowFirstPixelHue = 0;
+      for (int iteration = 0; iteration < 100; iteration++) {
+        robot.robotPeriodic();
+        var data = ledSim.getData();
+        for (int i = 0; i < 60; i++) {
+          final var hue = (rainbowFirstPixelHue + (i * 180 / 60)) % 180;
+          assertIndexColor(data, i, hue, 255, 128);
+        }
+        rainbowFirstPixelHue += 3;
+        rainbowFirstPixelHue %= 180;
+      }
+    }
+  }
+
+  private void assertIndexColor(byte[] data, int index, int hue, int saturation, int value) {
+    var color = new Color8Bit(Color.fromHSV(hue, saturation, value));
+    int b = data[index * 4];
+    int g = data[(index * 4) + 1];
+    int r = data[(index * 4) + 2];
+    int z = data[(index * 4) + 3];
+
+    assertAll(
+        () -> assertEquals(0, z),
+        () -> assertEquals(color.red, r & 0xFF),
+        () -> assertEquals(color.green, g & 0xFF),
+        () -> assertEquals(color.blue, b & 0xFF));
+  }
+}