Cucumber Background 使用指南

1. 概述

本文将深入讲解 Cucumber 中的 Background（背景） 机制。这是一个非常实用的功能，允许我们在每个测试场景（Scenario）执行前，自动运行一组预设的 Gherkin 语句。它的核心价值在于：减少重复、提升可读性、让测试更聚焦业务逻辑。

如果你经常写 Cucumber 测试，肯定遇到过这样的“踩坑”时刻：每个 Scenario 开头都得重复写一堆 Given 来准备测试数据，既啰嗦又难维护。Background 就是来解决这个问题的。

2. Cucumber Background 是什么

简单粗暴地说，Background 就是 Feature 级别的前置条件。它定义的步骤会在该 Feature 下的每一个 Scenario 之前自动执行。

为什么需要它？

我们以一个图书商店应用为例来说明。

先看核心业务类 BookStore：

public class BookStore {
    private List<Book> books = new ArrayList<>();
    
    public void addBook(Book book) {
        books.add(book);
    }
    
    public List<Book> booksByAuthor(String author) {
        return books.stream()
          .filter(book -> Objects.equals(author, book.getAuthor()))
          .collect(Collectors.toList());
    }

    public Optional<Book> bookByTitle(String title) {
        return books.stream()
          .filter(book -> book.getTitle().equals(title))
          .findFirst();
    }
}

再看对应的 Step Definitions：

public class BookStoreRunSteps {
    private BookStore store;
    private List<Book> foundBooks;
    private Book foundBook;
    
    @Before
    public void setUp() {
        store = new BookStore();
        foundBooks = new ArrayList<>();
    }
    
    @Given("^I have the following books in the store$")
    public void haveBooksInTheStore(DataTable table) {
        List<List<String>> rows = table.asLists(String.class);

        for (List<String> columns: rows) {
            store.addBook(new Book(columns.get(0), columns.get(1)));
        }
    }
    
    @When("^I search for books by author (.+)$")
    public void searchForBooksByAuthor(String author) {
        foundBooks = store.booksByAuthor(author);
    }

    @When("^I search for a book titled (.+)$")
    public void searchForBookByTitle(String title) {
        foundBook = store.bookByTitle(title).orElse(null);
    }
    
    @Then("^I find (\\d+) books$")
    public void findBooks(int count) {
        assertEquals(count, foundBooks.size());
    }

    @Then("^I find a book$")
    public void findABook() {
        assertNotNull(foundBook);
    }

    @Then("^I find no book$")
    public void findNoBook() {
        assertNull(foundBook);
    }
}

有了这些，我们就可以写 Feature 文件了。但如果没有 Background，会是这样：

Feature: Book Store Without Background
  Scenario: Find books by author
    Given I have the following books in the store
      | The Devil in the White City          | Erik Larson |
      | The Lion, the Witch and the Wardrobe | C.S. Lewis  |
      | In the Garden of Beasts              | Erik Larson |
    When I search for books by author Erik Larson
    Then I find 2 books

  Scenario: Find books by author, but isn't there
    Given I have the following books in the store
      | The Devil in the White City          | Erik Larson |
      | The Lion, the Witch and the Wardrobe | C.S. Lewis  |
      | In the Garden of Beasts              | Erik Larson |
    When I search for books by author Marcel Proust
    Then I find 0 books

  Scenario: Find book by title
    Given I have the following books in the store
      | The Devil in the White City          | Erik Larson |
      | The Lion, the Witch and the Wardrobe | C.S. Lewis  |
      | In the Garden of Beasts              | Erik Larson |
    When I search for a book titled The Lion, the Witch and the Wardrobe
    Then I find a book

  Scenario: Find book by title, but isn't there
    Given I have the following books in the store
      | The Devil in the White City          | Erik Larson |
      | The Lion, the Witch and the Wardrobe | C.S. Lewis  |
      | In the Garden of Beasts              | Erik Larson |
    When I search for a book titled Swann's Way
    Then I find no book

✅ 问题很明显：

数据初始化重复了 4 次
如果要加一本新书，得改 4 个地方
测试逻辑被大量 setup 步骤淹没，不够清晰

这就是 Background 的用武之地。

3. 实际应用示例

使用 Background 的方式非常简单：在 Feature 文件中，使用 Background 关键字定义一个“背景”块，放在所有 Scenario 之前。

Feature: Book Store With Background
  Background: The Book Store
    Given I have the following books in the store
      | The Devil in the White City          | Erik Larson |
      | The Lion, the Witch and the Wardrobe | C.S. Lewis  |
      | In the Garden of Beasts              | Erik Larson |

  Scenario: Find books by author
    When I search for books by author Erik Larson
    Then I find 2 books

  Scenario: Find books by author, but isn't there
    When I search for books by author Marcel Proust
    Then I find 0 books

  Scenario: Find book by title
    When I search for a book titled The Lion, the Witch and the Wardrobe
    Then I find a book

  Scenario: Find book by title, but isn't there
    When I search for a book titled Swann's Way
    Then I find no book

✅ 优化效果立竿见影：

每个 Scenario 只保留核心测试逻辑
数据初始化集中管理，一处修改，全局生效
Feature 文件可读性大幅提升，业务意图一目了然

⚠️ 注意：Background 中的步骤会在每一个 Scenario 之前执行。如果某个 Scenario 不需要这些前置数据，那它可能不适合放在这个 Feature 里，或者需要重新设计。

4. Background 与 @Before Hook 的区别

这是个高频面试题，也是实际开发中容易混淆的点。

对比项	Cucumber Background	@Before Hook
定义位置	Feature 文件（`.feature`）	Java 代码（Step Class）
可见性	✅ 非技术人员（如产品经理）也能看到	❌ 隐藏在代码中，不可见
维护性	✅ 修改测试数据无需动代码	❌ 需要改 Java 代码
执行时机	在每个 Scenario 的 Given 之前	在每个 Scenario 开始前（由 Cucumber 执行）
适用场景	业务相关的前置条件（如初始化测试数据）	技术相关的初始化（如数据库连接、Mock 设置）

📌 核心结论：

✅ 用 Background 来表达“业务上下文”，比如“用户已登录”、“购物车中有商品”。
✅ 用 @Before 来处理“技术细节”，比如重置测试对象、初始化服务依赖。

简单说：让业务逻辑可见，让技术细节隐藏。

5. 总结

✅ Background 是提升 Cucumber 测试可维护性和可读性的利器，尤其适合处理重复的 Given 步骤。
✅ 它让测试的业务逻辑更加聚焦，减少样板代码。
✅ 与 @Before 相比，最大的优势是透明性——所有 Stakeholder 都能看到测试的前置条件。
⚠️ 合理使用，避免滥用。如果 Background 过于复杂，可能意味着这个 Feature 职责过重，需要拆分。

示例代码已托管至 GitHub：https://github.com/baeldung/testing-examples/tree/main/cucumber-background-demo

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