Fakes vs Spies

Developers should learn and use fakes when they need to test components in isolation from external dependencies that are slow, unreliable, or difficult to set up, such as network services or complex databases meets developers should use spies when writing unit tests to monitor interactions with dependencies, such as external apis, databases, or other modules, without stubbing or mocking their actual implementation. Here's our take.

Fakes

Nice Pick

Developers should learn and use fakes when they need to test components in isolation from external dependencies that are slow, unreliable, or difficult to set up, such as network services or complex databases

Pros

• This is particularly useful in unit testing to ensure fast, repeatable tests without side effects, and in integration testing to simulate external systems during development or in CI/CD pipelines
• Related to: unit-testing, test-doubles

Cons

• Specific tradeoffs depend on your use case

Spies

Developers should use spies when writing unit tests to monitor interactions with dependencies, such as external APIs, databases, or other modules, without stubbing or mocking their actual implementation

Pros

• This is particularly useful for testing that certain functions are invoked as expected in scenarios like event handling, logging, or communication between components
• Related to: unit-testing, test-doubles

Cons

• Specific tradeoffs depend on your use case

The Verdict

These tools serve different purposes. Fakes is a methodology while Spies is a concept. We picked Fakes based on overall popularity, but your choice depends on what you're building.

The Bottom Line

Fakes wins

Based on overall popularity. Fakes is more widely used, but Spies excels in its own space.