What are the benefits and drawbacks of using jasmine mocks over real objects?

1 What are mocks and spies?

Mocks and spies are two types of test doubles that jasmine provides. A test double is an object that replaces a real object in a test, and can be controlled and inspected by the test. A mock is a test double that has predefined expectations and behavior, and can verify if those expectations are met. A spy is a test double that wraps a real object or function, and can record how it is called, with what arguments, and what it returns. You can also stub or modify the behavior of a spy if needed.

2 Why use mocks and spies?

One of the main benefits of using mocks and spies is that they can isolate your code under test from external dependencies and side effects. For example, if your code interacts with a database, a network, or a third-party service, you can use a mock or a spy to avoid actually calling those resources, and instead return fake data or responses. This can make your tests faster, more reliable, and more focused on the logic of your code. Another benefit of using mocks and spies is that they can help you test scenarios that are hard or impossible to reproduce with real objects, such as errors, failures, timeouts, or edge cases. You can use a mock or a spy to simulate these situations and check how your code handles them.

3 How to use mocks and spies?

To use mocks and spies in jasmine, you can use the jasmine.createSpy, jasmine.createSpyObj, and spyOn functions. These functions allow you to create mocks and spies for functions, objects, or methods, and configure their behavior and expectations. For example, you can use jasmine.createSpy to create a mock function that returns a specific value, or spyOn to create a spy that wraps an existing function and tracks its calls. You can also use jasmine.any, jasmine.anything, and jasmine.objectContaining to match arguments or return values with any type, any value, or an object with specific properties. To verify your mocks and spies, you can use the toHaveBeenCalled, toHaveBeenCalledWith, toHaveBeenCalledTimes, and toHaveReturnedWith matchers, among others.

4 What are the drawbacks of mocks and spies?

While mocks and spies can be very useful for testing, they also have some drawbacks that you should be aware of. One of the drawbacks is that they can introduce complexity and maintenance overhead to your tests. If you use too many mocks and spies, or if you make them too specific or too general, you may end up with tests that are hard to read, understand, or update. Another drawback is that they can create false positives or false negatives in your tests. If you use mocks and spies that do not match the behavior or interface of the real objects, you may end up with tests that pass when they should fail, or fail when they should pass. This can lead to bugs or errors in your code that are not detected by your tests.

5 How to avoid pitfalls of mocks and spies?

To avoid the pitfalls of mocks and spies, you should follow some best practices and guidelines when using them. One of them is to use mocks and spies sparingly and only when necessary. You should prefer real objects over mocks and spies whenever possible, especially if they are simple, stable, or fast. Another one is to use mocks and spies that are consistent and realistic with the real objects. You should avoid mocking or spying on things that you do not own or control, such as built-in objects, libraries, or frameworks. You should also avoid mocking or spying on private or internal details of your code, such as variables, functions, or methods that are not part of the public interface. You should also update your mocks and spies whenever you change your code or dependencies, and use tools or techniques that can help you automate or simplify this process.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?