[commands] Add RepeatCommand (#4009)

Co-authored-by: Starlight220 <53231611+Starlight220@users.noreply.github.com>

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

@@ -0,0 +1,62 @@
+// 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.
+
+#include "CommandTestBase.h"
+#include "frc2/command/FunctionalCommand.h"
+#include "frc2/command/RepeatCommand.h"
+
+using namespace frc2;
+class RepeatCommandTest : public CommandTestBase {};
+
+TEST_F(RepeatCommandTest, CallsMethodsCorrectly) {
+  CommandScheduler scheduler = GetScheduler();
+
+  int initCounter = 0;
+  int exeCounter = 0;
+  int isFinishedCounter = 0;
+  int endCounter = 0;
+  bool isFinishedHook = false;
+
+  auto command =
+      FunctionalCommand([&initCounter] { initCounter++; },
+                        [&exeCounter] { exeCounter++; },
+                        [&endCounter](bool interrupted) { endCounter++; },
+                        [&isFinishedCounter, &isFinishedHook] {
+                          isFinishedCounter++;
+                          return isFinishedHook;
+                        })
+          .Repeat();
+
+  EXPECT_EQ(0, initCounter);
+  EXPECT_EQ(0, exeCounter);
+  EXPECT_EQ(0, isFinishedCounter);
+  EXPECT_EQ(0, endCounter);
+
+  scheduler.Schedule(&command);
+  EXPECT_EQ(1, initCounter);
+  EXPECT_EQ(0, exeCounter);
+  EXPECT_EQ(0, isFinishedCounter);
+  EXPECT_EQ(0, endCounter);
+
+  isFinishedHook = false;
+  scheduler.Run();
+  EXPECT_EQ(1, initCounter);
+  EXPECT_EQ(1, exeCounter);
+  EXPECT_EQ(1, isFinishedCounter);
+  EXPECT_EQ(0, endCounter);
+
+  isFinishedHook = true;
+  scheduler.Run();
+  EXPECT_EQ(2, initCounter);
+  EXPECT_EQ(2, exeCounter);
+  EXPECT_EQ(2, isFinishedCounter);
+  EXPECT_EQ(1, endCounter);
+
+  isFinishedHook = false;
+  scheduler.Run();
+  EXPECT_EQ(2, initCounter);
+  EXPECT_EQ(3, exeCounter);
+  EXPECT_EQ(3, isFinishedCounter);
+  EXPECT_EQ(1, endCounter);
+}