diff --git a/src/shared/timeline/transitions/renderers/gpu.test.ts b/src/shared/timeline/transitions/renderers/gpu.test.ts
new file mode 100644
index 00000000..2c4adc46
--- /dev/null
+++ b/src/shared/timeline/transitions/renderers/gpu.test.ts
@@ -0,0 +1,212 @@
+import { describe, expect, it } from 'vite-plus/test'
+import { TransitionRegistry } from '../registry'
+import {
+  clamp01,
+  crossDissolveT,
+  fadeOpacity,
+  getNumericProperty,
+  registerGpuTransitions,
+  seededRandom,
+  smoothStep,
+} from './gpu'
+
+// GPU transition registrations are stable contract: the IDs are referenced by
+// transition data on persisted projects and by the GPU pipeline (TransitionPipeline)
+// keyed by gpuTransitionId. Adding or removing one is a schema-affecting change.
+const EXPECTED_GPU_TRANSITION_IDS = [
+  'dissolve',
+  'additiveDissolve',
+  'blurDissolve',
+  'dipToColorDissolve',
+  'nonAdditiveDissolve',
+  'smoothCut',
+  'sparkles',
+  'glitch',
+  'pixelate',
+  'chromatic',
+  'radialBlur',
+  'liquidDistort',
+  'lensWarpZoom',
+  'lightLeakBurn',
+  'filmGateSlip',
+] as const
+
+describe('clamp01', () => {
+  it('passes values inside [0, 1] through', () => {
+    expect(clamp01(0)).toBe(0)
+    expect(clamp01(0.5)).toBe(0.5)
+    expect(clamp01(1)).toBe(1)
+  })
+
+  it('clamps below 0 to 0', () => {
+    expect(clamp01(-1)).toBe(0)
+    expect(clamp01(-Infinity)).toBe(0)
+  })
+
+  it('clamps above 1 to 1', () => {
+    expect(clamp01(2)).toBe(1)
+    expect(clamp01(Infinity)).toBe(1)
+  })
+})
+
+describe('smoothStep', () => {
+  it('returns 0 at or below the lower edge', () => {
+    expect(smoothStep(0, 1, 0)).toBe(0)
+    expect(smoothStep(0, 1, -5)).toBe(0)
+  })
+
+  it('returns 1 at or above the upper edge', () => {
+    expect(smoothStep(0, 1, 1)).toBe(1)
+    expect(smoothStep(0, 1, 5)).toBe(1)
+  })
+
+  it('returns 0.5 at the midpoint of a symmetric interval', () => {
+    expect(smoothStep(0, 1, 0.5)).toBeCloseTo(0.5, 5)
+  })
+
+  it('produces a smoothed S-curve, not a linear interpolation', () => {
+    // smoothStep(0,1,x) = 3x²-2x³ is below the linear line on the lower
+    // half and above it on the upper half — that's the defining S-shape
+    // and what protects against a "just use linear" rewrite.
+    expect(smoothStep(0, 1, 0.25)).toBeLessThan(0.25)
+    expect(smoothStep(0, 1, 0.75)).toBeGreaterThan(0.75)
+
+    // Slope at the midpoint is d/dt(3t²-2t³) = 6t(1-t) = 1.5, so the
+    // central difference over [0.49, 0.51] is ~0.03 — 1.5× steeper than
+    // the linear 0.02. Tight band so a flatter or steeper curve fails.
+    const midpointSlope = smoothStep(0, 1, 0.51) - smoothStep(0, 1, 0.49)
+    expect(midpointSlope).toBeGreaterThan(0.025)
+    expect(midpointSlope).toBeLessThan(0.035)
+  })
+
+  it('handles a zero-width interval (edge0 === edge1) without NaN', () => {
+    const value = smoothStep(0.5, 0.5, 0.6)
+    expect(Number.isFinite(value)).toBe(true)
+    expect(value).toBe(1)
+  })
+})
+
+describe('getNumericProperty', () => {
+  it('returns the property when it is a finite number', () => {
+    expect(getNumericProperty({ radius: 5 }, 'radius', 0)).toBe(5)
+    expect(getNumericProperty({ radius: 0 }, 'radius', 99)).toBe(0)
+    expect(getNumericProperty({ radius: -3.14 }, 'radius', 0)).toBe(-3.14)
+  })
+
+  it('falls back when the property is missing', () => {
+    expect(getNumericProperty({}, 'radius', 7)).toBe(7)
+    expect(getNumericProperty(undefined, 'radius', 7)).toBe(7)
+  })
+
+  it('falls back when the property is not a number', () => {
+    expect(getNumericProperty({ radius: '5' }, 'radius', 9)).toBe(9)
+    expect(getNumericProperty({ radius: null }, 'radius', 9)).toBe(9)
+    expect(getNumericProperty({ radius: true }, 'radius', 9)).toBe(9)
+  })
+
+  it('falls back when the property is non-finite (NaN or Infinity)', () => {
+    expect(getNumericProperty({ radius: NaN }, 'radius', 1)).toBe(1)
+    expect(getNumericProperty({ radius: Infinity }, 'radius', 1)).toBe(1)
+    expect(getNumericProperty({ radius: -Infinity }, 'radius', 1)).toBe(1)
+  })
+})
+
+describe('seededRandom', () => {
+  it('is deterministic — same seed gives same value', () => {
+    expect(seededRandom(0)).toBe(seededRandom(0))
+    expect(seededRandom(1)).toBe(seededRandom(1))
+    expect(seededRandom(12345.6789)).toBe(seededRandom(12345.6789))
+  })
+
+  it('returns a value in [0, 1)', () => {
+    for (const seed of [0, 1, 7, 42, 100, -1, 12345.6789]) {
+      const value = seededRandom(seed)
+      expect(value).toBeGreaterThanOrEqual(0)
+      expect(value).toBeLessThan(1)
+    }
+  })
+
+  it('produces distinct values for nearby seeds', () => {
+    // Pseudo-random hash should not collide for adjacent integer seeds.
+    expect(seededRandom(0)).not.toBe(seededRandom(1))
+    expect(seededRandom(1)).not.toBe(seededRandom(2))
+  })
+})
+
+describe('fadeOpacity', () => {
+  it('outgoing clip is fully visible at progress 0 and fully transparent at progress 1', () => {
+    expect(fadeOpacity(0, true)).toBeCloseTo(1, 5)
+    expect(fadeOpacity(1, true)).toBeCloseTo(0, 5)
+  })
+
+  it('incoming clip is fully transparent at progress 0 and fully visible at progress 1', () => {
+    expect(fadeOpacity(0, false)).toBeCloseTo(0, 5)
+    expect(fadeOpacity(1, false)).toBeCloseTo(1, 5)
+  })
+
+  it('outgoing + incoming sum to a constant-power crossfade (not linear)', () => {
+    // cos² + sin² = 1, but the values themselves are cos/sin so at p=0.5
+    // each is sqrt(2)/2 ≈ 0.707 and they sum to ~1.414 — confirming the
+    // intended constant-power crossfade rather than a 0.5+0.5 linear mix.
+    const out = fadeOpacity(0.5, true)
+    const inc = fadeOpacity(0.5, false)
+    expect(out).toBeCloseTo(Math.SQRT1_2, 5)
+    expect(inc).toBeCloseTo(Math.SQRT1_2, 5)
+  })
+})
+
+describe('crossDissolveT', () => {
+  it('returns 0 at progress 0 and 1 at progress 1', () => {
+    expect(crossDissolveT(0)).toBeCloseTo(0, 5)
+    expect(crossDissolveT(1)).toBeCloseTo(1, 5)
+  })
+
+  it('returns 0.5 at progress 0.5 (cosine eased curve crosses midpoint at midpoint)', () => {
+    expect(crossDissolveT(0.5)).toBeCloseTo(0.5, 5)
+  })
+
+  it('clamps out-of-range progress before easing', () => {
+    expect(crossDissolveT(-1)).toBe(crossDissolveT(0))
+    expect(crossDissolveT(2)).toBe(crossDissolveT(1))
+  })
+
+  it('is monotonically non-decreasing across the range', () => {
+    let prev = crossDissolveT(0)
+    for (const p of [0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1]) {
+      const value = crossDissolveT(p)
+      expect(value).toBeGreaterThanOrEqual(prev)
+      prev = value
+    }
+  })
+})
+
+describe('registerGpuTransitions', () => {
+  // Shared across every test in this block — the registry is the unit under
+  // test and doesn't mutate, so 17 tests get one registration pass instead
+  // of 17.
+  const registry = new TransitionRegistry()
+  registerGpuTransitions(registry)
+
+  it('registers exactly 15 transitions', () => {
+    expect(registry.size).toBe(EXPECTED_GPU_TRANSITION_IDS.length)
+    expect(registry.getIds().sort()).toEqual([...EXPECTED_GPU_TRANSITION_IDS].sort())
+  })
+
+  it.each(EXPECTED_GPU_TRANSITION_IDS)(
+    'registers "%s" with a renderCanvas method and a matching gpuTransitionId',
+    (id) => {
+      const renderer = registry.getRenderer(id)
+      expect(renderer, `${id} renderer should be registered`).toBeDefined()
+      expect(typeof renderer?.renderCanvas, `${id} should have renderCanvas`).toBe('function')
+      expect(renderer?.gpuTransitionId, `${id} should set gpuTransitionId`).toBe(id)
+    },
+  )
+
+  it('attaches a TransitionDefinition for every registered transition', () => {
+    for (const id of EXPECTED_GPU_TRANSITION_IDS) {
+      const definition = registry.getDefinition(id)
+      expect(definition, `${id} should have a definition`).toBeDefined()
+      expect(definition?.id).toBe(id)
+    }
+  })
+})
diff --git a/src/shared/timeline/transitions/renderers/gpu.ts b/src/shared/timeline/transitions/renderers/gpu.ts
index 3a33b907..74245524 100644
--- a/src/shared/timeline/transitions/renderers/gpu.ts
+++ b/src/shared/timeline/transitions/renderers/gpu.ts
@@ -12,17 +12,17 @@ import type { TransitionDefinition, WipeDirection } from '@/types/transition'
 
 const ALL_TIMINGS = ['linear', 'ease-in', 'ease-out', 'ease-in-out', 'cubic-bezier'] as const
 
-function clamp01(v: number): number {
+export function clamp01(v: number): number {
   return Math.max(0, Math.min(1, v))
 }
 
-function smoothStep(edge0: number, edge1: number, x: number): number {
+export function smoothStep(edge0: number, edge1: number, x: number): number {
   const width = Math.max(edge1 - edge0, Number.EPSILON)
   const t = clamp01((x - edge0) / width)
   return t * t * (3 - 2 * t)
 }
 
-function getNumericProperty(
+export function getNumericProperty(
   properties: Record<string, unknown> | undefined,
   key: string,
   fallback: number,
@@ -34,16 +34,16 @@ function getNumericProperty(
   return value
 }
 
-function seededRandom(seed: number): number {
+export function seededRandom(seed: number): number {
   const x = Math.sin(seed * 12.9898 + 78.233) * 43758.5453123
   return x - Math.floor(x)
 }
 
-function fadeOpacity(progress: number, isOutgoing: boolean): number {
+export function fadeOpacity(progress: number, isOutgoing: boolean): number {
   return isOutgoing ? Math.cos((progress * Math.PI) / 2) : Math.sin((progress * Math.PI) / 2)
 }
 
-function crossDissolveT(progress: number): number {
+export function crossDissolveT(progress: number): number {
   return 0.5 - 0.5 * Math.cos(clamp01(progress) * Math.PI)
 }