Snapshot Testing
With Jest
Greg Douglas
@gwshark0
What Is Jest?
-
A JavaScript testing framework
-
Developed and used by Facebook
-
Available via npm
Why Use Jest?
-
It is Fast
-
It requires very little configuration
-
It has a great CLI and watch mode
-
It has clear and concise error messages
-
Snapshot tests
Snapshot Tests?
- Generate serialized snapshots from a test
- The snapshots are automatically written to a file
- No manual assertions necessary
- Subsequent executions of the test compare the current result against the saved snapshot
- Changes are made by updating the snapshot
- Snapshots are then committed to version control
DEMO
Why?
Advantages
- Easy (trivial) to write
- Reduces friction for writing tests
- Documents object / component structure
- Good for testing visual or "spatial" objects
- Great for code that changes frequently
Disadvantages
- Not as suited for testing complex functional logic
- Cannot do traditional TDD (red/green/refactor)
- Cannot do non-deterministic (random) tests
- Requires vigilance on the tester's part
- Noise from small changes and versioning
Another tool in the Toolbox.
QUESTIONS?
Snapshot Testing With Jest
By unicode
