Go TDD Patterns & Best Practices

Table-driven tests in Go structure multiple test cases in a slice of structs, each containing inputs and expected outputs. Loop through cases with `t.Run()` to execute each scenario independently, reducing code duplication and improving coverage across edge cases.

Use `require` for critical assertions that should stop the test immediately on failure, preventing cascading errors. Use `assert` to continue executing remaining checks, allowing you to see all failures in a single test run.

Isolate external dependencies—databases, APIs, network services—by defining interfaces and passing mock implementations into your code. This prevents unit tests from relying on external systems and ensures fast, reliable test execution.

Integration tests verify interactions between components and external systems using real or containerized dependencies. Unlike unit tests, they require setup of databases or services, use build tags to separate from unit tests, and run less frequently in CI/CD pipelines.

Yes. Refactor existing code to be testable by extracting dependencies into interfaces, then write tests using table-driven patterns and testify assertions. This gradual approach improves test coverage and code reliability without rewriting everything at once.

TDD best practices require testing both happy paths and error scenarios: invalid inputs, nil values, timeout cases, and dependency failures. Use table-driven tests to systematically cover each error type with distinct test cases and verify correct error types with `require.ErrorIs()`.