Add Unit Tests for eraserTest Function in @excalidraw/excalidraw/eraser #10274
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Added unit tests CT1 to CT7 to validate EraserTrail behavior with rectangles, lines (open and polygon), and arrows. Mocks for @excalidraw/element and @excalidraw/math ensure isolated, predictable testing without relying on DOM or complex calculations. TO-DOs included for future coverage of groups, bound text, containers, freedraw, zoom/stroke extremes, and minimal paths.
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Description
This pull request introduces a comprehensive suite of unit tests for the eraserTest function, which is part of the Eraser module in the Excalidraw project. The goal is to improve test coverage and ensure the correctness of the eraser’s behavior when interacting with various element types on the canvas.
The eraserTest function determines whether a segment of the eraser path intersects or affects an element, deciding whether it should be removed. It is a core part of the EraserTrail feature, responsible for interactive element deletion.
Changes Introduced
Added a new test file: packages/excalidraw/tests/eraser.test.tsx
Implemented 7 new test cases (CT1–CT7) covering different interaction scenarios between the eraser and elements:
- Rectangles, lines (open and closed), arrows, and polygons.
- Both positive (element should be erased) and negative (element should remain) cases.
Created mock modules to isolate behavior:
- @excalidraw/element mock for simplified geometry and element checks (isArrowElement, isLineElement, shouldTestInside, etc.).
- @excalidraw/math mock for geometric operations like lineSegmentsDistance and polygonIncludesPointNonZero.
Included TODO comments for future improvements such as testing grouped elements, linked text, zoom variations, and complex FreeDraw cases.
Test Results
All newly implemented tests passed successfully.
The number of tested functions nearly tripled, and over half of the eraser module’s logic is now covered by automated tests. Although branch coverage percentage decreased due to a higher number of conditional paths being tracked, the total tested logic increased substantially.
Next Steps (TO-DO)
Add tests for:
References
Function under test: eraserTest
Test implementation: eraser.test.tsx
Commit: 3230a82