At MetaMask, we are committed to delivering high-quality software. A key aspect of achieving this goal is through a robust testing strategy that includes both end-to-end (e2e), integration and unit tests. This document provides comprehensive guidelines on each testing type, emphasizing the importance of choosing the right test for the right scenario and detailing the specific practices for writing and organizing these tests.
Unit testing is a conceptually vague practice, as there is no consensus on how they should be written and what they should test. But in general, as outlined by Martin Fowler, there are two common approaches: solitary unit tests and sociable unit tests. At MetaMask, we employ both of these types of unit tests (see discussion on the use cases of each type). Unit tests examine individual components or functions in isolation or within their immediate context. At MetaMask we encourage a flexible approach to unit testing, recognizing the spectrum between sociable and solitary unit tests.
All components or functions should be validated through unit tests. These tests focus on the component's or function's internal logic and functionality. If UI integration tests are available, those are preferred for page-level components. However, developers may choose to write sociable unit tests for specific scenarios where UI integration tests might not be necessary or practical.
Best Practices: Follow the unit test best practices.
UI integration tests evaluate the interaction between multiple components within the application, ensuring they work together as intended. For MetaMask, we are aiming to make UI integration tests particularly focused on page-level components and are conducted in the context of the full UI application.
UI integration tests should be written for page-level components. These tests should simulate user journeys and validate the application's behavior in a full app context.
Best Practices: Follow the ui integration tests best practices.
End-to-end tests simulate real user scenarios from start to finish, testing the application as a whole. In the Extension, end-to-end tests are tests that strive to test a real extension app (including background, contentscript and ui processes) in a controlled environment from a user perspective.
End-to-end tests exercise an application's integration with external systems or services through critical user journeys. This includes any interactions between the UI, background process, dapp, blockchain, etc. End-to-end tests should closely mimic real user actions and flows.
Best Practices: Follow the end-to-end test best practices.
- Code fencing: Code fencing is available in MetaMask Extension and Mobile codebases. Though useful for its purposes, this practice is very problematic for unit/UI integration testing. We should avoid it.
To sum up, understanding the distinction between end-to-end, UI integration and unit tests and applying them appropriately is crucial for maintaining MetaMask's code quality and reliability. UI integration tests offer a broad view of user interactions and system integration for page-level components, while unit tests provide detailed insights into the functionality of individual components, and end-to-end tests validate the application's overall behavior, ensuring readiness for production. By following these guidelines, developers can ensure comprehensive test coverage, contributing to the robustness and user satisfaction of the application