Rezi Write Tests

When to use

Use this skill when:

• Writing tests for Rezi widgets or components
• Testing app state logic (reducers)
• Testing keybinding resolvers
• Need snapshot-style output assertions

Source of truth

• packages/core/src/testing/ — test utilities (createTestRenderer, etc.)
• packages/core/src/widgets/__tests__/ — existing widget tests (use as examples)
• packages/core/src/widgets/__tests__/composition.animationHooks.test.ts — animation hook test patterns
• packages/core/src/app/__tests__/widgetRenderer.transition.test.ts — ui.box transition expectations
• scripts/run-tests.mjs — test runner
• packages/core/src/testing/snapshot.ts — golden frame snapshot utilities (captureSnapshot, serializeSnapshot, diffSnapshots)
• scripts/rezi-snap.mjs — CLI for snapshot capture and verification

Steps

1. Create test file in the appropriate __tests__/ directory

2. Use createTestRenderer() for widget/render tests:

   import { describe, it } from "node:test";
   import * as assert from "node:assert/strict";
   import { createTestRenderer, ui } from "@rezi-ui/core";
   
   describe("MyWidget", () => {
     it("renders correctly", () => {
       const r = createTestRenderer({ viewport: { cols: 80, rows: 24 } });
       const result = r.render(ui.text("hello"));
       assert.ok(result.findText("hello"));
     });
   });

3. Test state logic by testing reducer functions directly:

   it("increments count", () => {
     const state = reducer({ count: 0 }, { type: "increment" });
     assert.strictEqual(state.count, 1);
   });

4. Use result.toText() for snapshot-style assertions

5. Use result.findById() to locate specific nodes in the render tree

6. Use golden frame snapshots for visual regression:

   import { captureSnapshot, serializeSnapshot, diffSnapshots, parseSnapshot } from "@rezi-ui/core";
   
   const snapshot = captureSnapshot("my-scene", myView(state), { viewport: { cols: 80, rows: 24 }, theme }, "dark");
   const text = serializeSnapshot(snapshot);
   // Compare with stored snapshot using diffSnapshots()

7. Run snapshot CLI for bulk capture/verify:

   node scripts/rezi-snap.mjs --update    # Capture new snapshots
   node scripts/rezi-snap.mjs --verify    # Verify against stored

8. For animation features, cover:

   • mount value
   • retarget while running
   • cleanup on unmount (no timer leak)
   • property filtering (position / size / opacity) for ui.box transitions

9. For extended routed actions, verify UiEvent payloads for widgets that emit non-press actions:

   • checkbox emits action: "toggle" with checked
   • virtualList emits action: "select" with index
   • table emits action: "rowPress" with rowIndex
   • radio/select flows emit action: "change"

10. For animation hook behavior, test:

• supported easing presets (linear, quad, cubic) resolve as expected
• retargeted mid-flight runs continue smoothly without jumping
• looping sequences (loop: true) remain active and deterministic

Running tests

# Full suite
node scripts/run-tests.mjs

# Single file
node --test path/to/test.ts

Verification

• All new tests pass
• No existing tests broken
• Tests are deterministic (bounded timers/explicit waits, no randomness)
• Golden snapshots match expected output (if applicable)