[commands] Add unless() decorator (#4244)

wpilibNewCommands/src/test/java/edu/wpi/first/wpilibj2/command/CommandDecoratorTest.java

@@ -9,6 +9,7 @@ import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import edu.wpi.first.hal.HAL;
 import edu.wpi.first.wpilibj.simulation.SimHooks;
+import java.util.concurrent.atomic.AtomicBoolean;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.parallel.ResourceLock;
 
@@ -182,4 +183,24 @@ class CommandDecoratorTest extends CommandTestBase {
       assertTrue(scheduler.isScheduled(perpetual));
     }
   }
+
+  @Test
+  void unlessTest() {
+    try (CommandScheduler scheduler = new CommandScheduler()) {
+      AtomicBoolean unlessCondition = new AtomicBoolean(true);
+      AtomicBoolean hasRunCondition = new AtomicBoolean(false);
+
+      Command command =
+          new InstantCommand(() -> hasRunCondition.set(true)).unless(unlessCondition::get);
+
+      scheduler.schedule(command);
+      scheduler.run();
+      assertFalse(hasRunCondition.get());
+
+      unlessCondition.set(false);
+      scheduler.schedule(command);
+      scheduler.run();
+      assertTrue(hasRunCondition.get());
+    }
+  }
 }

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

@@ -5,6 +5,7 @@
 #include <frc/simulation/SimHooks.h>
 
 #include "CommandTestBase.h"
+#include "frc2/command/ConditionalCommand.h"
 #include "frc2/command/InstantCommand.h"
 #include "frc2/command/ParallelRaceGroup.h"
 #include "frc2/command/PerpetualCommand.h"
@@ -101,3 +102,24 @@ TEST_F(CommandDecoratorTest, Perpetually) {
 
   EXPECT_TRUE(scheduler.IsScheduled(&command));
 }
+
+TEST_F(CommandDecoratorTest, Unless) {
+  CommandScheduler scheduler = GetScheduler();
+
+  bool hasRun = false;
+  bool unlessBool = true;
+
+  auto command =
+      InstantCommand([&hasRun] { hasRun = true; }, {}).Unless([&unlessBool] {
+        return unlessBool;
+      });
+
+  scheduler.Schedule(&command);
+  scheduler.Run();
+  EXPECT_FALSE(hasRun);
+
+  unlessBool = false;
+  scheduler.Schedule(&command);
+  scheduler.Run();
+  EXPECT_TRUE(hasRun);
+}