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GraphQL APIs with Spring Boot · 课时

对 GraphQL 解析器进行单元测试

为 Spring Boot 中的 GraphQL 解析器和数据获取逻辑编写有效的单元测试。

对 GraphQL 解析器进行单元测试 是 CoddyKit 上的免费 GraphQL APIs with Spring Boot 课时。 这是第 1 节课，共 4 节。 你可以在下方免费阅读本课时的完整内容 — 然后在浏览器中使用内置代码编辑器和全天候 AI 导师进行实践。 这是 GraphQL APIs with Spring Boot 学习路径的一部分，你的进度在网页和 CoddyKit 应用中同步。 GraphQL APIs with Spring Boot 课程共包含 4 节课。

本课时的部分内容尚未翻译，以英文显示。

Why Unit Test Resolvers?

Unit testing is crucial for ensuring the reliability of your GraphQL API. When we unit test resolvers, we focus on testing individual components in isolation.

  • Isolation: We test a resolver without needing a running server or database.
  • Correctness: Verify the resolver's logic, argument handling, and data transformation.
  • Speed: Unit tests run very fast, providing quick feedback during development.

This lesson will guide you through writing effective unit tests for your Spring Boot GraphQL resolvers.

Spring Boot Resolver Overview

Before testing, let's briefly recall how resolvers are structured in Spring Boot. They are typically Spring @Controller components with methods annotated for GraphQL operations like @QueryMapping or @MutationMapping.

These methods often depend on other Spring @Service components to fetch or manipulate data, which is where mocking comes in handy for testing.

Setting Up Test Environment

For unit testing in Spring Boot, you'll primarily use JUnit 5 and Mockito. These are typically included by default with spring-boot-starter-test.

  • JUnit 5: The testing framework to write and run your tests.
  • Mockito: A mocking framework to create mock objects for dependencies, allowing you to isolate the resolver under test.

Ensure your pom.xml or build.gradle includes the spring-boot-starter-test dependency.

Isolating Resolvers with Mocks

Resolvers often interact with services, repositories, or other components. To unit test a resolver, we need to isolate it from these dependencies.

Mockito helps us create 'mock' objects that mimic the behavior of real dependencies. This allows us to control what the dependencies return and verify how they are called, without actually invoking their real logic.

  • @Mock: Creates a mock instance of a class or interface.
  • @InjectMocks: Injects the created mocks into the object being tested.
  • @ExtendWith(MockitoExtension.class): Integrates Mockito with JUnit 5.

Testing a Simple Resolver

Let's start with a basic resolver that doesn't have any external dependencies. We can instantiate it directly and call its method.

This example shows a simple resolver and its corresponding unit test using JUnit 5 assertions.

package com.example.app;

import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertEquals;

// Imagine MyResolver.java exists with a greeting() method
// @Controller
// public class MyResolver {
//   @QueryMapping
//   public String greeting() {
//     return "Hello GraphQL!";
//   }
// }

class MyResolverTest {
  @Test
  void greetingReturnsCorrectMessage() {
    // 1. Arrange: Create an instance of the resolver
    MyResolver resolver = new MyResolver();

    // 2. Act: Call the method under test
    String result = resolver.greeting();

    // 3. Assert: Verify the output
    assertEquals("Hello GraphQL!", result);
  }
}

Testing with Mocked Services

Most resolvers depend on services to perform business logic. Here's how to test a resolver that uses a GreetingService.

We use @Mock for the service and @InjectMocks for the resolver. Then, when().thenReturn() tells the mock what to return when its method is called.

package com.example.app;

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.junit.jupiter.MockitoExtension;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.mockito.Mockito.when;

// Imagine GreetingResolver.java and GreetingService.java exist
// (see previous scenes for context)

@ExtendWith(MockitoExtension.class)
class GreetingResolverTest {
  @Mock
  private GreetingService greetingService;

  @InjectMocks
  private GreetingResolver greetingResolver;

  @Test
  void personalizedGreetingReturnsExpected() {
    // Arrange: Define mock behavior
    when(greetingService.generateGreeting("Alice"))
      .thenReturn("Hello, Alice!");

    // Act: Call resolver method
    String result = greetingResolver.personalizedGreeting("Alice");

    // Assert: Verify resolver's output
    assertEquals("Hello, Alice!", result);
  }
}

Verifying Input Arguments

It's important to ensure that your resolver correctly passes arguments to its underlying services. Mockito's verify() method helps with this.

Mockito.verify(mockObject).method(expectedArgs) confirms that the specified method was called with the exact arguments during the test execution.

package com.example.app;

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.junit.jupiter.MockitoExtension;
import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.when;

@ExtendWith(MockitoExtension.class)
class GreetingResolverVerifyTest {
  @Mock
  private GreetingService greetingService;

  @InjectMocks
  private GreetingResolver greetingResolver;

  @Test
  void serviceCalledWithCorrectArgument() {
    // Arrange
    when(greetingService.generateGreeting("Bob"))
      .thenReturn("Hi Bob!");

    // Act
    greetingResolver.personalizedGreeting("Bob");

    // Assert: Verify service method was called with "Bob"
    verify(greetingService).generateGreeting("Bob");
  }
}

Testing for Expected Return Values

After a resolver processes data, it should return the correct output. JUnit's assertions are used to confirm these return values.

  • assertEquals(expected, actual): Checks if two values are equal.
  • assertNotNull(object): Checks if an object is not null.
  • assertTrue(condition): Checks if a condition is true.

Always assert the final state or return value of the resolver method.

package com.example.app;

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.junit.jupiter.MockitoExtension;
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.mockito.Mockito.when;

@ExtendWith(MockitoExtension.class)
class GreetingResolverAssertTest {
  @Mock
  private GreetingService greetingService;

  @InjectMocks
  private GreetingResolver greetingResolver;

  @Test
  void personalizedGreetingReturnsExpectedValue() {
    String name = "Charlie";
    String expectedGreeting = "Hello, Charlie!";

    // Arrange
    when(greetingService.generateGreeting(name))
      .thenReturn(expectedGreeting);

    // Act
    String actualGreeting = 
      greetingResolver.personalizedGreeting(name);

    // Assert
    assertEquals(expectedGreeting, actualGreeting);
  }
}

Testing Error Scenarios

Robust resolvers should handle errors gracefully. Unit tests can verify that your resolvers throw expected exceptions or handle them appropriately.

Use JUnit's assertThrows to confirm that a specific exception type is thrown when certain conditions are met, such as a service failing.

package com.example.app;

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.junit.jupiter.MockitoExtension;
import static org.junit.jupiter.api.Assertions.assertThrows;
import static org.mockito.Mockito.when;

@ExtendWith(MockitoExtension.class)
class ErrorHandlingResolverTest {
  @Mock
  private GreetingService greetingService;

  @InjectMocks
  private GreetingResolver greetingResolver;

  @Test
  void personalizedGreetingThrowsExceptionOnError() {
    String name = "ErrorUser";

    // Arrange: Mock service to throw an exception
    when(greetingService.generateGreeting(name))
      .thenThrow(new RuntimeException("Service failed"));

    // Act & Assert: Verify that the resolver throws
    assertThrows(RuntimeException.class, () -> {
      greetingResolver.personalizedGreeting(name);
    });
  }
}

Quick Check: Unit Test Concepts

When unit testing a Spring Boot GraphQL resolver that depends on a UserService, what is the primary purpose of using Mockito's @Mock annotation on the UserService instance within your test class?

Recap & What's Next

Congratulations! You've learned the fundamentals of unit testing your GraphQL resolvers in Spring Boot.

  • We understood the importance of isolation for unit tests.
  • We used Mockito to mock service dependencies.
  • We wrote tests to verify resolver logic, argument passing, and return values.
  • We also covered testing error scenarios.

By applying these techniques, you can ensure your GraphQL resolvers are robust and behave as expected. Next, you might explore integration testing to verify your entire GraphQL API end-to-end.

常见问题解答

「对 GraphQL 解析器进行单元测试」课时是免费的吗？

是的 — 「对 GraphQL 解析器进行单元测试」的完整文本可在网页上免费阅读。要进行交互式练习（内置代码编辑器和全天候 AI 导师）并解锁 GraphQL APIs with Spring Boot 课程的其余内容，请升级到 CoddyKit PRO。 GraphQL APIs with Spring Boot 课程共包含 4 节课。

「对 GraphQL 解析器进行单元测试」这节课中我会学到什么？

为 Spring Boot 中的 GraphQL 解析器和数据获取逻辑编写有效的单元测试。 你通过在浏览器中直接运行的动手代码来练习 GraphQL APIs with Spring Boot，全天候 AI 导师会在你学习这节课的过程中回答你的问题。

学习 GraphQL APIs with Spring Boot 需要有经验吗？

无需任何先前经验。CoddyKit 上的 GraphQL APIs with Spring Boot 课程适合初学者到高级学习者，你可以从这里开始或从头开始，按照自己的节奏学习。 这是第 1 节课，共 4 节。

「对 GraphQL 解析器进行单元测试」课时需要多长时间？

大多数 CoddyKit 课程大约需要 5–10 分钟。每节课都很精短且互动，所以你能稳步进步，并在网页和应用中从离开的地方继续。

我能在这节 GraphQL APIs with Spring Boot 课中编写并运行代码吗？

能。每节 GraphQL APIs with Spring Boot 课都包含内置代码编辑器，你可以在浏览器中直接编写并运行真实代码，并获得即时 AI 反馈 — 无需本地设置。

此课程中的所有课时

  1. 对 GraphQL 解析器进行单元测试
  2. 集成测试 GraphQL API
  3. 部署 Spring Boot GraphQL
  4. GraphQL API 的持续集成
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