[cmd3] Fix commandv3 builders and add tests (#8482)

Sequential group builder had an inverted if condition causing NPEs

Parallel group builder was building parallel groups using an old ctor
signature and creating groups that didn't match what was specified in
the builder

Test coverage has been added for both builder types

commandsv3/src/test/java/org/wpilib/command3/SequentialGroupBuilderTest.java

@@ -0,0 +1,108 @@
+// 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 org.wpilib.command3;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertInstanceOf;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+class SequentialGroupBuilderTest {
+  @Test
+  void andThenSingle() {
+    var c1 = Command.noRequirements().executing(Coroutine::park).named("C1");
+
+    var builder = new SequentialGroupBuilder();
+    var sequence = builder.andThen(c1).named("Seq");
+    assertInstanceOf(SequentialGroup.class, sequence);
+    assertEquals(List.of(c1), ((SequentialGroup) sequence).getCommands());
+    assertEquals("Seq", sequence.name());
+  }
+
+  @Test
+  void andThenMultiple() {
+    var c1 = Command.noRequirements().executing(Coroutine::park).named("C1");
+    var c2 = Command.noRequirements().executing(Coroutine::park).named("C2");
+
+    var builder = new SequentialGroupBuilder();
+    var sequence = builder.andThen(c1, c2).named("Seq");
+
+    assertInstanceOf(SequentialGroup.class, sequence);
+    assertEquals(List.of(c1, c2), ((SequentialGroup) sequence).getCommands());
+    assertEquals("Seq", sequence.name());
+  }
+
+  @Test
+  void andThenRepeated() {
+    var c1 = Command.noRequirements().executing(Coroutine::park).named("C1");
+    var c2 = Command.noRequirements().executing(Coroutine::park).named("C2");
+
+    var builder = new SequentialGroupBuilder();
+    var sequence = builder.andThen(c1).andThen(c2).named("Seq");
+
+    assertInstanceOf(SequentialGroup.class, sequence);
+    assertEquals(List.of(c1, c2), ((SequentialGroup) sequence).getCommands());
+    assertEquals("Seq", sequence.name());
+  }
+
+  @Test
+  void andThenSingleNull() {
+    var builder = new SequentialGroupBuilder();
+    assertThrows(NullPointerException.class, () -> builder.andThen((Command) null));
+  }
+
+  @Test
+  void andThenThenVarargNullArray() {
+    var builder = new SequentialGroupBuilder();
+    assertThrows(NullPointerException.class, () -> builder.andThen((Command[]) null));
+  }
+
+  @Test
+  void andThenNullInVarargs() {
+    var builder = new SequentialGroupBuilder();
+    assertThrows(NullPointerException.class, () -> builder.andThen((Command) null));
+  }
+
+  @Test
+  void untilReturnsParallelGroup() {
+    var c1 = Command.noRequirements().executing(Coroutine::park).named("C1");
+    var builder = new SequentialGroupBuilder();
+    var sequence = builder.andThen(c1).until(() -> false).named("Seq");
+    assertInstanceOf(ParallelGroup.class, sequence);
+    assertEquals("Seq", sequence.name());
+  }
+
+  @Test
+  void namedWithNull() {
+    var builder = new SequentialGroupBuilder();
+    assertThrows(NullPointerException.class, () -> builder.named(null));
+  }
+
+  @Test
+  void automaticNameWithEmptyGroup() {
+    var builder = new SequentialGroupBuilder();
+    var sequence = builder.withAutomaticName();
+    assertEquals("", sequence.name());
+  }
+
+  @Test
+  void automaticNameWithOneCommand() {
+    var c1 = Command.noRequirements().executing(Coroutine::park).named("C1");
+    var builder = new SequentialGroupBuilder();
+    var sequence = builder.andThen(c1).withAutomaticName();
+    assertEquals("C1", sequence.name());
+  }
+
+  @Test
+  void automaticNameWithMultipleCommands() {
+    var c1 = Command.noRequirements().executing(Coroutine::park).named("C1");
+    var c2 = Command.noRequirements().executing(Coroutine::park).named("C2");
+    var builder = new SequentialGroupBuilder();
+    var sequence = builder.andThen(c1, c2).withAutomaticName();
+    assertEquals("C1 -> C2", sequence.name());
+  }
+}