Debugging "property missing ':'" Error in Jest Snapshots with React, Emotion, and Jest-Emotion
This article addresses a common error encountered when using React, Emotion, and Jest for testing. We'll delve into the "property missing ':'" error during Jest snapshot testing and provide a clear solution.
Understanding the Issue
The error "property missing ':'" arises when Jest-Emotion attempts to parse CSS styles generated by Emotion. It indicates a syntax error within your CSS, specifically missing colons (:) in CSS property-value pairs. This usually happens when updating Emotion or Jest-Emotion versions without careful consideration.
Analyzing the Example
Let's examine the scenario provided:
- Reusable Components Repo: Utilizes Emotion 9.1.0, React-Emotion 9.1.0, Jest-Emotion 9.0.0, and React-Test-Renderer 16.6.3. All tests pass.
- Dashboard Repo: Uses Emotion 9.2.11, React-Emotion 9.2.11, Jest-Emotion 9.2.11, and React-Test-Renderer 16.6.3. One test fails with the "property missing ':'" error.
The key difference is the version of Emotion and related packages used in the Dashboard Repo. This suggests a potential incompatibility between newer Emotion versions and Jest-Emotion, or a change in how Emotion generates CSS.
Solution: Downgrading Jest-Emotion
The most effective solution is to downgrade Jest-Emotion in your Dashboard Repo to a version compatible with your current Emotion setup. The documentation for Jest-Emotion often lists supported Emotion versions.
Explanation
Jest-Emotion parses and prints CSS generated by Emotion in your tests. If Jest-Emotion expects a specific CSS syntax and Emotion generates styles in a different format (due to version differences), parsing errors occur. Downgrading Jest-Emotion aligns the parsing rules with the generated CSS, resolving the conflict.
Important Note:
Always refer to the official documentation of the libraries involved for the latest compatibility information and best practices.
Additional Tips
- Thorough Testing: Always perform comprehensive testing after updating any dependency to ensure compatibility and avoid unexpected errors.
- Version Control: Use version control systems (like Git) to easily revert to previous working versions if issues arise.
- Clear Communication: When working on a team, ensure clear communication about library versions to prevent such conflicts.
Conclusion
By understanding the root cause of the "property missing ':'" error and implementing the provided solution, you can effectively resolve snapshot testing issues with React, Emotion, and Jest. Remember to prioritize compatibility testing and stay informed about the latest version compatibility guidelines for your chosen libraries.
