在适用于 Rust 的 AWS SDK 中使用 aws-smithy-mocks 进行单元测试

适用于 Rust 的 AWS SDK 提供了多种方法来测试与 AWS 服务交互的代码。本主题介绍了如何使用 aws-smithy-mocks crate，它提供了一种简单而强大的方法来模拟 AWS SDK 客户端响应以用于测试目的。

概览

在为使用 AWS 服务的代码编写测试时，通常需要避免进行实际的网络调用。aws-smithy-mocks crate 提供了一种解决方案，支持：

添加依赖项

在项目目录的命令提示符中，将 aws-smithy-mocks crate 添加为依赖项：

$ cargo add --dev aws-smithy-mocks

使用 --dev 选项可将 crate 添加到 Cargo.toml 文件的 [dev-dependencies] 部分。作为开发依赖项，它不会被编译并包含在用于生产代码的最终二进制文件中。

此示例代码还使用 Amazon Simple Storage Service 作为示例 AWS 服务，并且需要功能 test-util。

$ cargo add aws-sdk-s3 --features test-util

这会将 crate 添加到 Cargo.toml 文件的 [dependencies] 部分。

基本用法

以下是一个简单的示例，展示了如何使用 aws-smithy-mocks 测试与 Amazon Simple Storage Service（Amazon S3）交互的代码：

use aws_sdk_s3::operation::get_object::GetObjectOutput;
use aws_sdk_s3::primitives::ByteStream;
use aws_smithy_mocks::{mock, mock_client};

#[tokio::test]
async fn test_s3_get_object() {
    // Create a rule that returns a successful response
    let get_object_rule = mock!(aws_sdk_s3::Client::get_object)
        .then_output(|| {
            GetObjectOutput::builder()
                .body(ByteStream::from_static(b"test-content"))
                .build()
        });

    // Create a mocked client with the rule
    let s3 = mock_client!(aws_sdk_s3, [&get_object_rule]);

    // Use the client as you would normally
    let result = s3
        .get_object()
        .bucket("test-bucket")
        .key("test-key")
        .send()
        .await
        .expect("success response");

    // Verify the response
    let data = result.body.collect().await.expect("successful read").to_vec();
    assert_eq!(data, b"test-content");

    // Verify the rule was used
    assert_eq!(get_object_rule.num_calls(), 1);
}

创建 mock 规则

规则是使用 mock! 宏创建的，该宏将客户端操作作为参数。然后，您可以配置规则的行为方式。

匹配请求

您可以通过匹配请求属性来使规则更加具体：

let rule = mock!(Client::get_object)
    .match_requests(|req| req.bucket() == Some("test-bucket") && req.key() == Some("test-key"))
    .then_output(|| {
        GetObjectOutput::builder()
            .body(ByteStream::from_static(b"test-content"))
            .build()
    });

不同的响应类型

您可以返回不同类型的响应：

// Return a successful response
let success_rule = mock!(Client::get_object)
    .then_output(|| GetObjectOutput::builder().build());

// Return an error
let error_rule = mock!(Client::get_object)
    .then_error(|| GetObjectError::NoSuchKey(NoSuchKey::builder().build()));

// Return a specific HTTP response
let http_rule = mock!(Client::get_object)
    .then_http_response(|| {
        HttpResponse::new(
            StatusCode::try_from(503).unwrap(),
            SdkBody::from("service unavailable")
        )
    });

测试重试行为

aws-smithy-mocks 最强大的功能之一是能够通过定义响应序列来测试重试行为：

// Create a rule that returns 503 twice, then succeeds
let retry_rule = mock!(aws_sdk_s3::Client::get_object)
    .sequence()
    .http_status(503, None)                          // First call returns 503
    .http_status(503, None)                          // Second call returns 503
    .output(|| GetObjectOutput::builder().build())   // Third call succeeds
    .build();

// With repetition using times()
let retry_rule = mock!(Client::get_object)
    .sequence()
    .http_status(503, None)
    .times(2)                                        // First two calls return 503
    .output(|| GetObjectOutput::builder().build())   // Third call succeeds
    .build();

规则模式

您可以使用规则模式控制规则的匹配和应用方式：

// Sequential mode: Rules are tried in order, and when a rule is exhausted, the next rule is used
let client = mock_client!(aws_sdk_s3, RuleMode::Sequential, [&rule1, &rule2]);

// MatchAny mode: The first matching rule is used, regardless of order
let client = mock_client!(aws_sdk_s3, RuleMode::MatchAny, [&rule1, &rule2]);

示例：测试重试行为

以下是一个更完整的示例，展示了如何测试重试行为：

use aws_sdk_s3::operation::get_object::GetObjectOutput;
use aws_sdk_s3::config::RetryConfig;
use aws_sdk_s3::primitives::ByteStream;
use aws_smithy_mocks::{mock, mock_client, RuleMode};

#[tokio::test]
async fn test_retry_behavior() {
    // Create a rule that returns 503 twice, then succeeds
    let retry_rule = mock!(aws_sdk_s3::Client::get_object)
        .sequence()
        .http_status(503, None)
        .times(2)
        .output(|| GetObjectOutput::builder()
            .body(ByteStream::from_static(b"success"))
            .build())
        .build();

    // Create a mocked client with the rule and custom retry configuration
    let s3 = mock_client!(
        aws_sdk_s3,
        RuleMode::Sequential,
        [&retry_rule],
        |client_builder| {
            client_builder.retry_config(RetryConfig::standard().with_max_attempts(3))
        }
    );

    // This should succeed after two retries
    let result = s3
        .get_object()
        .bucket("test-bucket")
        .key("test-key")
        .send()
        .await
        .expect("success after retries");

    // Verify the response
    let data = result.body.collect().await.expect("successful read").to_vec();
    assert_eq!(data, b"success");

    // Verify all responses were used
    assert_eq!(retry_rule.num_calls(), 3);
}

示例：基于请求参数的不同响应

您还可以创建规则，根据请求参数返回不同的响应：

use aws_sdk_s3::operation::get_object::{GetObjectOutput, GetObjectError};
use aws_sdk_s3::types::error::NoSuchKey;
use aws_sdk_s3::Client;
use aws_sdk_s3::primitives::ByteStream;
use aws_smithy_mocks::{mock, mock_client, RuleMode};

#[tokio::test]
async fn test_different_responses() {
    // Create rules for different request parameters
    let exists_rule = mock!(Client::get_object)
        .match_requests(|req| req.bucket() == Some("test-bucket") && req.key() == Some("exists"))
        .sequence()
        .output(|| GetObjectOutput::builder()
            .body(ByteStream::from_static(b"found"))
            .build())
        .build();

    let not_exists_rule = mock!(Client::get_object)
        .match_requests(|req| req.bucket() == Some("test-bucket") && req.key() == Some("not-exists"))
        .sequence()
        .error(|| GetObjectError::NoSuchKey(NoSuchKey::builder().build()))
        .build();

    // Create a mocked client with the rules in MatchAny mode
    let s3 = mock_client!(aws_sdk_s3, RuleMode::MatchAny, [&exists_rule, &not_exists_rule]);

    // Test the "exists" case
    let result1 = s3
        .get_object()
        .bucket("test-bucket")
        .key("exists")
        .send()
        .await
        .expect("object exists");

    let data = result1.body.collect().await.expect("successful read").to_vec();
    assert_eq!(data, b"found");

    // Test the "not-exists" case
    let result2 = s3
        .get_object()
        .bucket("test-bucket")
        .key("not-exists")
        .send()
        .await;

    assert!(result2.is_err());
    assert!(matches!(result2.unwrap_err().into_service_error(),
                    GetObjectError::NoSuchKey(_)));
}

最佳实践

使用 aws-smithy-mocks 进行测试时：