Initial

tests/unit/timeline.test.ts

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+import { describe, it, expect, beforeEach } from 'vitest';
+import { get } from 'svelte/store';
+// Import the store module directly: the feature barrel re-exports .svelte
+// components, which the unit runner (no Svelte plugin) cannot transform.
+import { timelineStore, positionAt } from '$features/timeline/store';
+
+beforeEach(() => {
+	timelineStore.pause();
+	timelineStore.setRange(0, 0);
+	timelineStore.setSpeed(1);
+	timelineStore.setMarkers([]);
+});
+
+describe('timelineStore', () => {
+	it('clamps seek to the current range', () => {
+		timelineStore.setRange(0, 10_000);
+		timelineStore.seek(99_999);
+		expect(get(timelineStore).time).toBe(10_000);
+		timelineStore.seek(-5);
+		expect(get(timelineStore).time).toBe(0);
+	});
+
+	it('clamps the current time when the range shrinks', () => {
+		timelineStore.setRange(0, 10_000);
+		timelineStore.seek(9_000);
+		timelineStore.setRange(0, 4_000);
+		expect(get(timelineStore).time).toBe(4_000);
+	});
+
+	it('ignores play when there is no duration', () => {
+		timelineStore.play();
+		expect(get(timelineStore).playing).toBe(false);
+	});
+
+	it('plays and pauses when a duration exists', () => {
+		timelineStore.setRange(0, 10_000);
+		timelineStore.play();
+		expect(get(timelineStore).playing).toBe(true);
+		timelineStore.pause();
+		expect(get(timelineStore).playing).toBe(false);
+	});
+
+	it('rewinds to min on reset', () => {
+		timelineStore.setRange(0, 10_000);
+		timelineStore.seek(7_000);
+		timelineStore.reset();
+		expect(get(timelineStore).time).toBe(0);
+		expect(get(timelineStore).playing).toBe(false);
+	});
+
+	it('stores the playback speed', () => {
+		timelineStore.setSpeed(5);
+		expect(get(timelineStore).speed).toBe(5);
+	});
+});
+
+describe('positionAt', () => {
+	const path: [number, number, ...number[]][] = [
+		[60, 100],
+		[62, 102],
+		[64, 104]
+	];
+
+	it('returns the first point at t=0 and the last at t=duration', () => {
+		expect(positionAt(path, 0, 1000)).toEqual([60, 100]);
+		expect(positionAt(path, 1000, 1000)).toEqual([64, 104]);
+	});
+
+	it('interpolates linearly between samples', () => {
+		// Quarter of the way = halfway along the first segment.
+		const p = positionAt(path, 250, 1000)!;
+		expect(p[0]).toBeCloseTo(61, 6);
+		expect(p[1]).toBeCloseTo(101, 6);
+	});
+
+	it('clamps outside the flight window and handles an empty path', () => {
+		expect(positionAt(path, -100, 1000)).toEqual([60, 100]);
+		expect(positionAt(path, 99_999, 1000)).toEqual([64, 104]);
+		expect(positionAt([], 0, 1000)).toBeNull();
+	});
+});