6 Examples of a Test Stub

John Spacey, updated on February 12, 2017

A test stub is quickly developed code that is used as a placeholder so that other sections of code can be unit tested. Test stubs typically return a hardcoded response that is in a valid format but completely static. They are useful for unit testing when dependencies aren't developed yet, aren't available, are unreliable, slow or difficult to setup with required test data. The following are illustrative examples.

Data Access

A stub for a data access object that isn't developed yet. Returns hardcoded values.

Integration

A developer uses a stub to simulate integration with systems that she can't connect to on her local environment.

Test Data

A developer uses a test stub to simulate a wide variety of responses from systems. For example, a developer may simulate rare response codes for a banking transaction that are difficult to arrange in development environments.

User Interface

A developer initially populates a web page with a hello world message to test that a redirect is working.

Stability

A module does frequent transactions with an external system that is often down. A developer implements a test stub to replace the calls to the system to increase the reliability of unit tests.

Speed

A software function involves algorithms that are computationally complex. A developer implements a test stub to temporarily replace such algorithms to speed their unit testing.

Overview: Test Stub
Type	Unit Testing Coding
Definition	Quickly developed code that is used as a placeholder to facilitate unit testing.
Value	Unit testing when dependencies aren't ready, are unstable, slow or difficult to setup with required data.
Related Concepts	Testing Unit Testing Test Automation Test Fixture Test Harness Test Drivers Mock Object