Feature 05 task 2: Core UI primitives (#34)

Co-authored-by: dev_agent <dev_agent@cubecraftlabs.com>
Co-committed-by: dev_agent <dev_agent@cubecraftlabs.com>

web/src/ui/Slider.test.tsx

@@ -0,0 +1,69 @@
+import { fireEvent, render, screen } from '@testing-library/react'
+import { useState } from 'react'
+import { describe, expect, it } from 'vitest'
+import { expectMinHitArea } from '../test/hitArea.ts'
+import { Slider } from './Slider.tsx'
+
+function Harness() {
+  const [value, setValue] = useState(0.7)
+  return (
+    <Slider
+      aria-label="Creativity (temperature)"
+      min={0}
+      max={1}
+      step={0.1}
+      value={value}
+      onChange={(event) => setValue(Number(event.target.value))}
+    />
+  )
+}
+
+describe('Slider', () => {
+  it('is a native slider exposing its range and value', () => {
+    render(<Harness />)
+    const slider = screen.getByRole('slider', { name: 'Creativity (temperature)' })
+    expect(slider).toHaveAttribute('type', 'range')
+    expect(slider).toHaveAttribute('min', '0')
+    expect(slider).toHaveAttribute('max', '1')
+    expect(slider).toHaveValue('0.7')
+  })
+
+  it('updates the grape fill with the value', () => {
+    render(<Harness />)
+    const slider = screen.getByRole('slider')
+    expect(slider.style.getPropertyValue('--slider-fill')).toBe('70%')
+    fireEvent.change(slider, { target: { value: '0.2' } })
+    expect(slider).toHaveValue('0.2')
+    expect(slider.style.getPropertyValue('--slider-fill')).toBe('20%')
+  })
+
+  it('has a ≥ 44 px hit area', () => {
+    render(<Harness />)
+    expectMinHitArea(screen.getByRole('slider'))
+  })
+
+  it('fails fast on an empty range', () => {
+    expect(() => render(<Slider aria-label="Bad" min={1} max={1} value={1} readOnly />)).toThrow(
+      'max (1) must be greater than min (1)',
+    )
+  })
+
+  it('accepts values at both ends of the range', () => {
+    render(
+      <>
+        <Slider aria-label="At min" min={0} max={1} value={0} readOnly />
+        <Slider aria-label="At max" min={0} max={1} value={1} readOnly />
+      </>,
+    )
+    expect(screen.getByRole('slider', { name: 'At min' }).style.getPropertyValue('--slider-fill')).toBe('0%')
+    expect(screen.getByRole('slider', { name: 'At max' }).style.getPropertyValue('--slider-fill')).toBe('100%')
+  })
+
+  it.each([
+    [2, 'value (2) must be within [0, 1]'],
+    [-0.1, 'value (-0.1) must be within [0, 1]'],
+    [Number.NaN, 'value (NaN) must be within [0, 1]'],
+  ])('fails fast when the value %s is outside the range', (value, message) => {
+    expect(() => render(<Slider aria-label="Bad" min={0} max={1} value={value} readOnly />)).toThrow(message)
+  })
+})