PatternTest.java

package com.hanserwei.patterns.command;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.assertThrows;
import static org.junit.jupiter.api.Assertions.assertTrue;

import org.junit.jupiter.api.Test;

/** 验证本模式的协作契约与边界行为. */
public final class PatternTest {
  /** 两次追加依次撤销到各自执行前状态. */
  @Test
  void undoesInReverseOrder() {
    TextEditor editor = new TextEditor();
    CommandHistory history = new CommandHistory();
    history.execute(new AppendCommand(editor, "Java"));
    history.execute(new AppendCommand(editor, " 25"));
    assertEquals("Java 25", editor.text());
    assertTrue(history.undo());
    assertEquals("Java", editor.text());
    assertTrue(history.undo());
    assertEquals("", editor.text());
    assertFalse(history.undo());
  }

  /** 执行失败不会额外增加历史条目. */
  @Test
  void excludesFailedExecution() {
    TextEditor editor = new TextEditor();
    Command command = new AppendCommand(editor, "Java");
    CommandHistory history = new CommandHistory();
    history.execute(command);
    assertThrows(IllegalStateException.class, () -> history.execute(command));
    assertTrue(history.undo());
    assertFalse(history.undo());
    assertEquals("", editor.text());
  }
}