The Go service runs locally, tests pass. Then you remember the tests are hitting the real Binance API. The next day, CI fails: rate limit exceeded, unstable network, or the exchange quietly renamed a field in its response. Tests that depend on external APIs are flaky at best, unusable in CI at worst. The problem is structural: exchanges don't have usable sandbox environments (Binance testnet exists, but with constraints that make automated integration testing difficult), rate limits are aggressive, and some operations like PlaceOrder have real side effects. A different approach is needed. The problem with external APIs in tests Three concrete reasons you can't test against real exchange APIs in CI: Rate limits : Binance caps at 1200 requests/minute on the order book endpoint. Ten developers running tests in parallel, and the first ones get banned.…