7 Examples of Mock Objects

John Spacey, updated on February 12, 2017

Mock objects are components that implement the same interface as real components but simulate their implementation. The following are illustrative examples.

Unavailable Objects

Developers commonly test their code as they write it. In the context of a project or sprint, there are often dependencies that aren't available yet. Mock objects may be developed as disposable placeholders.

Integration

Integration to systems and services may be replaced with mock objects to speed development. This may be done because such integrations are unavailable or unreliable in certain environments.

Speed

Replacing slow objects with fast simulations.

Scenarios

Mock objects may simulate scenarios and data that are difficult to produce with real objects.

Predictability

Replacing non-deterministic objects with a specific or predictable result set. For example, a mock object may replace a random number generator with a specific set of numbers.

Testing Inputs

One of the primary differences between a mock object and a test stub is that mock objects tend to have expectations. For example, they may validate inputs. This can be useful for testing scenarios such as integration where you want to make sure you're sending valid requests.

Destructive Testing

Replacing real objects with objects that behave badly to test non-functional requirements such as reliability and resilience.

Overview: Mock Objects
Type	Coding Unit Testing
Definition	Objects that implement the same interface as real objects but simulate their implementation.
Value	Testing Replacing unavailable, troublesome, unpredictable or slow objects in particular environments.
Related Concepts	Unit Testing Test Automation Test Stub