The problem with mocks is that they test your assumptions, not reality...
When you mock a CRM client to return one account, you're assuming it always returns one account, that IDs have a particular format, that there's no pagination, that all fields are populated. Each assumption is a place where production could behave differently whilst your tests stay green
Your contract tests use cached JSON fixtures. Salesforce changes a field type, your contract test still passes (old fixture), your mocks return the wrong type, production breaks. You've now got three test layers (contract, mock scenarios, E2E) where two can lie to you. All your contract and mock tests won't save you. Production will still go down
I have zero confidence in these types of tests. Integration tests and E2E tests against real infrastructure give me actual confidence. They're slower, but they tell you the truth. Want to test rate limiting? Use real rate limits. Want to test missing data? Delete the data.
Slow tests that tell the truth beat fast tests that lie. That said, fast tests are valuable for developer productivity. The trade-off is whether you want speed or confidence
When you mock a CRM client to return one account, you're assuming it always returns one account, that IDs have a particular format, that there's no pagination, that all fields are populated. Each assumption is a place where production could behave differently whilst your tests stay green
Your contract tests use cached JSON fixtures. Salesforce changes a field type, your contract test still passes (old fixture), your mocks return the wrong type, production breaks. You've now got three test layers (contract, mock scenarios, E2E) where two can lie to you. All your contract and mock tests won't save you. Production will still go down
I have zero confidence in these types of tests. Integration tests and E2E tests against real infrastructure give me actual confidence. They're slower, but they tell you the truth. Want to test rate limiting? Use real rate limits. Want to test missing data? Delete the data.
Slow tests that tell the truth beat fast tests that lie. That said, fast tests are valuable for developer productivity. The trade-off is whether you want speed or confidence