Fix C++ POVButton (#2294)

Also add unit test.

wpilibNewCommands/src/test/native/cpp/frc2/command/POVButtonTest.cpp

@@ -0,0 +1,47 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2020 FIRST. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include <frc/Joystick.h>
+#include <mockdata/DriverStationData.h>
+
+#include "CommandTestBase.h"
+#include "frc2/command/CommandScheduler.h"
+#include "frc2/command/RunCommand.h"
+#include "frc2/command/WaitUntilCommand.h"
+#include "frc2/command/button/POVButton.h"
+#include "gtest/gtest.h"
+
+using namespace frc2;
+class POVButtonTest : public CommandTestBase {};
+
+TEST_F(POVButtonTest, SetPOVTest) {
+  HAL_JoystickPOVs povs;
+  povs.count = 1;
+  povs.povs[0] = 0;
+  HALSIM_SetJoystickPOVs(1, &povs);
+  HALSIM_NotifyDriverStationNewData();
+
+  auto& scheduler = CommandScheduler::GetInstance();
+  bool finished = false;
+
+  WaitUntilCommand command([&finished] { return finished; });
+
+  frc::Joystick joy(1);
+  POVButton(&joy, 90).WhenPressed(&command);
+  scheduler.Run();
+  EXPECT_FALSE(scheduler.IsScheduled(&command));
+
+  povs.povs[0] = 90;
+  HALSIM_SetJoystickPOVs(1, &povs);
+  HALSIM_NotifyDriverStationNewData();
+
+  scheduler.Run();
+  EXPECT_TRUE(scheduler.IsScheduled(&command));
+  finished = true;
+  scheduler.Run();
+  EXPECT_FALSE(scheduler.IsScheduled(&command));
+}