Feature Request: Add Snapshot Testing to Fossil Test

[dreamer-coding]

Is your feature request related to a problem? Please describe.

Developers often need to validate outputs such as strings, JSON, or structured data against a previously approved version to ensure that changes in the code don’t unintentionally alter expected outputs. Without snapshot testing, manually verifying such outputs is time-consuming and error-prone.

Describe the solution you’d like

Integrate snapshot testing functionality into Fossil Test to automatically capture, store, and compare test outputs.

Features:
1. Snapshot Storage
• Store snapshots as files in a dedicated directory (e.g., snapshots/).
• Use test names to name snapshot files (e.g., test_function_output.snap).
• Allow storage in a custom directory via configuration.
2. Snapshot Matching
• Automatically compare current outputs with stored snapshots during test runs.
• Mark tests as failed if snapshots don’t match.
• Show a detailed diff highlighting mismatched lines.
3. Snapshot Management Commands
• --snapshot-update: Approve and overwrite snapshots with the new output.
• --snapshot-clean: Remove unused or outdated snapshots.
• CLI prompt to approve updates interactively when differences are detected (optional).
4. Data Format
• Support structured (e.g., JSON, XML) and unstructured data (e.g., strings, text files).
• Allow custom serializers and deserializers for non-text formats.
5. Integration
• Seamlessly integrate into existing Fossil Test workflows.
• Ensure compatibility with Fossil Mock for testing outputs from mocked components.
6. Reporting
• Show snapshot test results in the final test summary.
• Include snapshots in unified reporting for Fossil Test and Fossil Mock.

Describe alternatives you’ve considered
1. Manual Validation:
Developers manually check outputs by saving files and diffing them with tools like diff or git. This is tedious and not automated.
2. Custom Assertions:
Using custom assertions to check outputs against stored files. This provides partial automation but lacks integration with test frameworks.

Additional Context
• Use Cases:
• Validating API responses against known outputs.
• Checking console logs or error messages for consistency.
• Testing UI rendering outputs (e.g., HTML or JSON structures).
• Implementation Notes:
• Consider storing snapshot metadata (e.g., test environment details) alongside the snapshot.
• Offer options to ignore whitespace or specific fields when comparing snapshots.