Open-Source Testing · m-radzikowski

aws-sdk-client-mock

aws-sdk-client-mock is a TypeScript library for mocking AWS SDK v3 clients in unit tests. It provides a fluent, type-safe API to define mock behavior for specific commands and payloads, with support for spying on calls and Jest matchers.

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Source: GitHub — github.com/m-radzikowski/aws-sdk-client-mock

905

GitHub stars

Forks

TypeScript

Primary language

MIT

License (OSI-approved)

Key facts

Objective fields from the source. Values we can't verify are shown as “Unknown” rather than guessed.

Field	Value
Repository	m-radzikowski/aws-sdk-client-mock
Owner	m-radzikowski
Primary language	TypeScript
License	MIT — OSI-approved
Stars	905
Forks	49
Open issues	31
Latest release	v4.1.0 (2024-10-15)
Last updated	2026-01-29
Source	https://github.com/m-radzikowski/aws-sdk-client-mock

What aws-sdk-client-mock is

A modular mocking library for @aws-sdk/* clients using a command-based matching system. Supports fluent chaining, payload-based behavior matching, consecutive call sequences (resolvesOnce/rejectsOnce), custom callbacks, and integration with Jest/Vitest assertion libraries.

Quickstart

Get the aws-sdk-client-mock source

Clone the repository and explore it locally.

terminalbash

1git clone https://github.com/m-radzikowski/aws-sdk-client-mock.git2cd aws-sdk-client-mock3# follow the project's README for install & configuration

Need it deployed, integrated, or customized instead? DEV.co ships production installs.

Best use cases

Lambda function testing

Mock AWS service calls (SNS, DynamoDB, S3) within Lambda handlers to isolate business logic and avoid integration test overhead.

Microservice unit tests

Test application code that consumes AWS services without requiring live credentials or integration test infrastructure.

Payment/financial transaction workflows

Mock SQS, SNS, and DynamoDB interactions to test event-driven architectures and message processing pipelines in isolation.

Implementation considerations

Requires AWS SDK v3.363.0 or later; verify version compatibility with project dependencies to avoid @smithy/types conflicts.
Mock setup/teardown must be explicit (mockClient, restore, reset); use Jest/Vitest lifecycle hooks (beforeEach/afterEach) to prevent test pollution.
Payload matching is partial by default; enable strict: true for exact payload matching to catch unintended parameter variations.
Chained behaviors (resolvesOnce/rejectsOnce) execute in definition order; verify test expectations align with call sequence.
Type safety is enforced at compile time; IDE/TypeScript catch many mistakes, but runtime behavior requires test execution.

When to avoid it — and what to weigh

SDK v2 dependency — This library targets AWS SDK v3 only. Legacy applications using SDK v2 (@aws-sdk/js) will require a different mocking approach or SDK upgrade.
Integration/end-to-end testing required — Mocks hide real AWS service behavior, regional limits, and eventual consistency issues. Integration tests against a test AWS environment remain necessary.
Non-AWS SDK AWS interactions — This library only mocks official AWS SDK clients. Custom HTTP clients or third-party AWS wrappers will need alternative mocking strategies.
Browser-only environments without Node.js — Primarily designed for Node.js and Electron; browser-only environments may have limited or untested support.

License & commercial use

MIT License. Permissive open-source license allowing commercial use, modification, and distribution with attribution.

MIT License explicitly permits commercial use without restriction. No known limitations on proprietary application usage. No commercial support tier documented in the repository; reliance on community/GitHub issues.

DEV.co evaluation signals

Editorial assessment — not user reviews. Directional, with an explicit confidence level.

Signal	Assessment
Maintenance	Active
Documentation	Strong
License clarity	Clear
Deployment complexity	Low
DEV.co fit	Strong
Assessment confidence	High

Security considerations

No real AWS credentials or network calls occur during mocking, reducing test environment security risk. Mocks may mask real AWS error conditions (throttling, permission denial) that production code should handle; integration tests remain necessary for security-sensitive workflows.

Alternatives to consider

jest-mock-aws-sdk

Older Jest-only mocking approach; lacks fluent API, type safety, and active maintenance compared to aws-sdk-client-mock.

AWS SDK v3 LocalStack/MinIO

Local service emulation for integration tests; higher setup complexity but captures real service behavior and is unsuitable for fast unit tests.

Manual jest.mock() or test doubles

Requires custom boilerplate; loses type safety and lacks payload-based matching, matchers, and spy convenience.

Software development agency

Build on aws-sdk-client-mock with DEV.co software developers

Install aws-sdk-client-mock via npm and review the GitHub README for fluent API examples, or contact us to discuss integration into your test strategy.

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aws-sdk-client-mock FAQ

Does this mock work with AWS SDK v2?

No. aws-sdk-client-mock is designed exclusively for AWS SDK v3 (@aws-sdk/* modular clients). SDK v2 users need alternative mocking libraries or must upgrade.

Can I mock custom AWS SDK configuration or credentials?

The mock intercepts command execution, bypassing configuration. Test configuration code separately via integration tests or use getClient() callback in callsFake() to inspect client state.

What happens if I don't specify a mock behavior?

By default, mocked Client#send() returns undefined. Use .onAnyCommand().resolves({}) or .resolves({}) to define a catch-all default.

Does this library require AWS credentials?

No. Mocking intercepts all command execution before credential validation, so no credentials, network access, or AWS account access is needed.

Software developers & web developers for hire

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Ready to mock AWS services in your tests?

Install aws-sdk-client-mock via npm and review the GitHub README for fluent API examples, or contact us to discuss integration into your test strategy.

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