Error Testing for JSON APIs in Phoenix with ExUnit

When building backend systems, handling the happy path is only half the battle. To build resilient applications, you must ensure your JSON APIs respond gracefully when things go wrong, without exposing sensitive internal details or corrupting database state. This text-based course guides you through writing reliable, automated error tests for JSON-based APIs using ExUnit within Phoenix applications. You will learn to validate error payloads, handle validation failures, and assert correct HTTP status codes under failure conditions. What you'll learn: - Understand the core architecture of Phoenix error handling and how ExUnit interacts with the test database. - Write assertions for common HTTP error states including bad requests, unauthorized access, and resource-not-found scenarios. - Test database integrity by asserting that database transactions roll back correctly during failed API operations. - Structure JSON error responses to maintain consistent payload schemas for API consumers. - Implement modern Elixir testing practices, including using sandbox databases and mocking external dependencies safely. We begin with foundational concepts of error management in Elixir and Phoenix, establishing a solid vocabulary before moving on to practical testing patterns. You will read through step-by-step implementations of ExUnit test cases, dissecting common API failure modes and learning how to assert against them. This course is designed for beginner to intermediate backend developers who have a basic understanding of Elixir and Phoenix but want to build confidence in their automated testing strategies. No advanced testing experience is required. Start writing cleaner, more resilient API tests today.