PatternTest.java

package com.hanserwei.patterns.memento;

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 {
  /** 多级快照按逆序恢复，而不是共享最新的可变状态. */
  @Test
  void restoresIndependentSnapshots() {
    Editor editor = new Editor();
    History history = new History(editor);
    history.checkpoint();
    editor.write("A");
    history.checkpoint();
    editor.write("AB");
    assertTrue(history.undo());
    assertEquals("A", editor.text());
    assertTrue(history.undo());
    assertEquals("", editor.text());
    assertFalse(history.undo());
  }

  /** 一个编辑器不能恢复另一个编辑器的快照. */
  @Test
  void rejectsForeignSnapshot() {
    Editor first = new Editor();
    Editor second = new Editor();
    assertThrows(IllegalArgumentException.class, () -> second.restore(first.save()));
  }
}