1. 概述
在这个简短的教程中，我们将介绍Cucumber中的Background，这是一个允许我们为Cucumber Feature的每次测试执行一些语句的功能。
2. Cucumber Background
首先，让我们解释一下Cucumber Background是什么。它的目的是在每次运行Feature之前执行一个或多个语句。
但是Background在这里试图解决的问题是什么呢？
假设我们有一个想要使用Cucumber进行测试的书店应用程序。首先，让我们创建该应用程序，它只是一个Java类：
public class BookStore {
private final List<Book> books = new ArrayList<>();
public void addBook(Book book) {
books.add(book);
}
public void addAllBooks(Collection<Book> books) {
this.books.addAll(books);
}
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();
}
}
如我们所见，可以在BookStore中添加和搜索Book对象。现在，让我们创建一些Cucumber语句来与BookStore交互：
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);
}
}
通过这些语句定义，我们可以添加Book对象，按作者姓名或书名搜索Book，并检查Book是否存在。
接下来可以创建我们的Feature文件。我们可以按作者名搜索书籍，也可以按书名搜索书籍：
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
这个Feature测试可以正常运行，但它似乎有点冗长，因为我们为每个测试初始化测试数据。这不仅会重复很多行，而且如果我们想要更新测试数据，则必须为每个测试执行此操作。这就是Cucumber Background的用武之地。
3. 例子
那么，如何为这个Feature通过Background创建测试数据呢？为此，我们必须使用关键字Background，给它起一个标题，就像我们为Scenario所做的那样，并定义要执行的语句：
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 |
完成此操作后，我们可以去掉之前Feature文件中每个测试的Given子句，让测试的定义专注于自己的功能，而不包含任何数据定义：
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
正如我们所看到的，现在的Feature文件比以前简单地多。
4. 与@Before的区别
现在，让我们讨论Cucumber Background和@Before钩子之间的区别。钩子还允许我们在场景之前执行代码，但是这些代码对那些只阅读Feature文件的人是隐藏的。另一方面，Background由Feature文件中可见的语句组成。
5. 总结
在这篇简短的文章中，我们学习了如何使用Cucumber的Background功能。它允许我们在功能的每个场景之前执行一些语句。我们还讨论了此功能与@Before钩子之间的区别。
与往常一样，本教程的完整源代码可在GitHub上获得。
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