[commands] Add DeferredCommand (#5566)

Allows commands to be constructed at runtime without proxying.

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

@@ -0,0 +1,85 @@
+// 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.wpilibj2.command;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.only;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import java.util.Set;
+import java.util.function.Supplier;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
+
+class DeferredCommandTest extends CommandTestBase {
+  @ParameterizedTest
+  @ValueSource(booleans = {true, false})
+  void deferredFunctionsTest(boolean interrupted) {
+    MockCommandHolder innerCommand = new MockCommandHolder(false);
+    DeferredCommand command = new DeferredCommand(innerCommand::getMock, Set.of());
+
+    command.initialize();
+    verify(innerCommand.getMock()).initialize();
+
+    command.execute();
+    verify(innerCommand.getMock()).execute();
+
+    assertFalse(command.isFinished());
+    verify(innerCommand.getMock()).isFinished();
+
+    innerCommand.setFinished(true);
+    assertTrue(command.isFinished());
+    verify(innerCommand.getMock(), times(2)).isFinished();
+
+    command.end(interrupted);
+    verify(innerCommand.getMock()).end(interrupted);
+  }
+
+  @SuppressWarnings("unchecked")
+  @Test
+  void deferredSupplierOnlyCalledDuringInit() {
+    try (CommandScheduler scheduler = new CommandScheduler()) {
+      Supplier<Command> supplier = (Supplier<Command>) mock(Supplier.class);
+      when(supplier.get()).thenReturn(Commands.none(), Commands.none());
+
+      DeferredCommand command = new DeferredCommand(supplier, Set.of());
+      verify(supplier, never()).get();
+
+      scheduler.schedule(command);
+      verify(supplier, only()).get();
+      scheduler.run();
+
+      scheduler.schedule(command);
+      verify(supplier, times(2)).get();
+    }
+  }
+
+  @Test
+  void deferredRequirementsTest() {
+    Subsystem subsystem = new Subsystem() {};
+    DeferredCommand command = new DeferredCommand(Commands::none, Set.of(subsystem));
+
+    assertTrue(command.getRequirements().contains(subsystem));
+  }
+
+  @Test
+  void deferredNullCommandTest() {
+    DeferredCommand command = new DeferredCommand(() -> null, Set.of());
+    assertDoesNotThrow(
+        () -> {
+          command.initialize();
+          command.execute();
+          command.isFinished();
+          command.end(false);
+        });
+  }
+}