github.com/stretchr/testify

Testify is a testing toolkit I've used across dozens of Go projects, primarily for its assert and require packages. From a security perspective, it's refreshingly low-risk: it's purely a test-time dependency with no runtime exposure, no network operations, no crypto implementation, and no external dependencies beyond the standard library. The supply chain risk is minimal.

The assert package provides clear, readable test failures with helpful diffs, while require stops test execution immediately on failure—crucial for preventing cascading errors that might mask security issues in tests. The mock package is adequate for basic mocking, though I find it verbose for complex interfaces. Suite support helps organize integration tests, but I rarely use it for security-critical code where explicit test isolation is clearer.

One practical caveat: testify's error messages can leak sensitive data if you're not careful about what you pass to assertions. Always sanitize or use custom comparators when testing with secrets, tokens, or PII. The library won't protect you from logging sensitive values in test output.

Testify is the de facto standard for Go test assertions and mocking. The assert and require packages provide readable test code without sacrificing performance - assertions compile to simple conditionals with helpful error output. The suite package is useful for managing shared test fixtures, though we've found the startup/teardown hooks can mask resource leaks if not carefully implemented.

The mock package works well for interface mocking with call expectations, though generating mocks still requires external tooling (mockery). One gotcha: require stops test execution immediately while assert continues, which matters when debugging cascading failures. We've standardized on require to fail fast and avoid noisy logs from dependent assertions.

The library has minimal runtime impact - it's just syntactic sugar over testing.T methods. Breaking changes between major versions are rare and well-documented. The http assertion helpers (assert.HTTPSuccess, etc.) save boilerplate but don't replace proper integration testing patterns. Overall, it reduces test verbosity without introducing complexity or performance concerns.

Testify has been a mainstay in my Go projects for years. The assert and require packages are straightforward - assert continues on failure while require halts immediately, giving you control over test flow. The API is intuitive and error messages are clear enough to debug failures quickly. Memory footprint is negligible since it's test-only code, and I've never seen performance issues even in massive test suites.

The mock package is functional but verbose - you'll write a lot of boilerplate setting up expectations. It works reliably for simple cases but complex mock scenarios get unwieldy fast. The suite package adds setup/teardown hooks which is useful, but be cautious: suites don't play nicely with parallel tests and can hide test interdependencies if you're not careful about state management.

One gotcha: the assert functions return booleans indicating pass/fail, which means forgotten if-checks can let tests continue when they shouldn't. Using require for critical assertions avoids this. The library is stable with rare breaking changes, making upgrades smooth. Documentation could be better organized, but the API surface is small enough that you'll learn it quickly through usage.