Testing
The ApprovalTests library is the canonical implementation of approval testing, available across Java, .NET, JavaScript, Python, Ruby, and PHP. It handles the mechanics of capturing output, managing approved/received files, and opening diff tools—leaving you to focus on what to test. This guide covers practical usage across the three
Approval Testing
Microservice architectures distribute the blast radius of API changes across multiple teams and deployment pipelines. A field renamed in the user service breaks the order service, which breaks the notification service, and nobody finds out until three services are deployed and the monitoring lights up. The standard advice is "
Testing
What do you do when you can't write an expected value for your assertion? When the output is a complex JSON object, a rendered report, a formatted table, or an entire HTML page—and writing expect(output).toBe(...) would require typing out hundreds of lines? Approval testing solves
Approval Testing
The problem with complex outputs isn't that they're hard to test — it's that the obvious way to test them is wrong. When your API endpoint returns a JSON object with twenty fields, the instinct is to assert on each one: assertEquals(result.status, "
Testing Strategy
Approval testing is a technique where you test by comparing actual output to a previously "approved" expected output—stored as a file on disk. Instead of writing assert result == "some string", you write Approvals.verify(result) and the framework handles the comparison. The first time a