test(01-01): add failing tests for palette module

- Tests cover all 7 CategoryType values with 3 shades each
- Tests for headerGradient returning valid CSSProperties with linear-gradient
- Tests for overviewHeaderGradient multi-stop gradient
- Tests for amountColorClass: income, available, and expense paths

frontend/src/lib/palette.test.ts

@@ -0,0 +1,137 @@
+import { describe, it, expect } from 'vitest'
+import {
+  palette,
+  CategoryType,
+  headerGradient,
+  overviewHeaderGradient,
+  amountColorClass,
+} from './palette'
+
+describe('palette exports', () => {
+  it('exports all 7 CategoryType values', () => {
+    const expectedTypes: CategoryType[] = [
+      'income',
+      'bill',
+      'variable_expense',
+      'debt',
+      'saving',
+      'investment',
+      'carryover',
+    ]
+    expectedTypes.forEach((type) => {
+      expect(palette[type]).toBeDefined()
+    })
+  })
+
+  it('has exactly 7 entries', () => {
+    expect(Object.keys(palette)).toHaveLength(7)
+  })
+
+  it('each category has light, medium, and base shades', () => {
+    Object.entries(palette).forEach(([, shades]) => {
+      expect(shades.light).toBeTruthy()
+      expect(shades.medium).toBeTruthy()
+      expect(shades.base).toBeTruthy()
+    })
+  })
+
+  it('all shade values are non-empty oklch strings', () => {
+    Object.entries(palette).forEach(([, shades]) => {
+      expect(shades.light).toMatch(/oklch/)
+      expect(shades.medium).toMatch(/oklch/)
+      expect(shades.base).toMatch(/oklch/)
+    })
+  })
+})
+
+describe('headerGradient', () => {
+  it('returns a CSSProperties object for a valid category type', () => {
+    const result = headerGradient('bill')
+    expect(result).toBeDefined()
+    expect(typeof result).toBe('object')
+  })
+
+  it('returns an object with a background property', () => {
+    const result = headerGradient('income')
+    expect(result).toHaveProperty('background')
+  })
+
+  it('background value is a linear-gradient', () => {
+    const result = headerGradient('bill')
+    expect(String(result.background)).toMatch(/linear-gradient/)
+  })
+
+  it('gradient uses the light and medium shades of the category', () => {
+    const result = headerGradient('saving')
+    expect(String(result.background)).toContain(palette.saving.light)
+    expect(String(result.background)).toContain(palette.saving.medium)
+  })
+})
+
+describe('overviewHeaderGradient', () => {
+  it('returns a CSSProperties object', () => {
+    const result = overviewHeaderGradient()
+    expect(result).toBeDefined()
+    expect(typeof result).toBe('object')
+  })
+
+  it('returns an object with a background property', () => {
+    const result = overviewHeaderGradient()
+    expect(result).toHaveProperty('background')
+  })
+
+  it('background value is a multi-stop linear-gradient', () => {
+    const result = overviewHeaderGradient()
+    const bg = String(result.background)
+    expect(bg).toMatch(/linear-gradient/)
+    // Should have multiple color stops (at least 3 commas after the direction)
+    const stops = bg.split('oklch').length - 1
+    expect(stops).toBeGreaterThanOrEqual(3)
+  })
+})
+
+describe('amountColorClass', () => {
+  it('returns text-success for positive income (isIncome=true, actual > 0)', () => {
+    expect(amountColorClass({ type: 'income', actual: 100, budgeted: 0, isIncome: true })).toBe(
+      'text-success'
+    )
+  })
+
+  it('returns empty string for zero income (isIncome=true, actual = 0)', () => {
+    expect(amountColorClass({ type: 'income', actual: 0, budgeted: 0, isIncome: true })).toBe('')
+  })
+
+  it('returns text-warning when actual > budgeted (over-budget expense)', () => {
+    expect(amountColorClass({ type: 'bill', actual: 200, budgeted: 100 })).toBe('text-warning')
+  })
+
+  it('returns empty string when actual equals budgeted (exactly on budget)', () => {
+    expect(amountColorClass({ type: 'bill', actual: 100, budgeted: 100 })).toBe('')
+  })
+
+  it('returns empty string when actual < budgeted (under budget)', () => {
+    expect(amountColorClass({ type: 'bill', actual: 50, budgeted: 100 })).toBe('')
+  })
+
+  it('returns empty string when isAvailable=true and actual is zero', () => {
+    expect(amountColorClass({ type: 'bill', actual: 0, budgeted: 0, isAvailable: true })).toBe('')
+  })
+
+  it('returns text-success when isAvailable=true and actual > 0', () => {
+    expect(
+      amountColorClass({ type: 'bill', actual: 500, budgeted: 0, isAvailable: true })
+    ).toBe('text-success')
+  })
+
+  it('returns text-destructive when isAvailable=true and actual < 0', () => {
+    expect(
+      amountColorClass({ type: 'bill', actual: -100, budgeted: 0, isAvailable: true })
+    ).toBe('text-destructive')
+  })
+
+  it('returns text-destructive for negative income (isIncome=true, actual < 0)', () => {
+    expect(
+      amountColorClass({ type: 'income', actual: -50, budgeted: 0, isIncome: true })
+    ).toBe('text-destructive')
+  })
+})