feat: implement Contribution Replay Timeline (Phase 9)

components/dashboard/ContributionForecast.test.tsx

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+import { render, screen } from '@testing-library/react';
+import { describe, it, expect, vi } from 'vitest';
+import ContributionForecast from './ContributionForecast';
+import type { ActivityData } from '@/types/dashboard';
+
+// Mock framer-motion to prevent animation issues during testing
+vi.mock('framer-motion', () => ({
+  motion: {
+    div: ({ children, className, whileHover, ...props }: any) => (
+      <div className={className} {...props}>
+        {children}
+      </div>
+    ),
+  },
+}));
+
+// Mock lucide-react
+vi.mock('lucide-react', () => ({
+  TrendingUp: () => <div data-testid="trending-up" />,
+  TrendingDown: () => <div data-testid="trending-down" />,
+  Minus: () => <div data-testid="minus" />,
+  Sparkles: () => <div data-testid="sparkles" />,
+  Calendar: () => <div data-testid="calendar" />,
+  Zap: () => <div data-testid="zap" />,
+  LineChart: () => <div data-testid="line-chart" />,
+  Activity: () => <div data-testid="activity" />,
+  Target: () => <div data-testid="target" />,
+}));
+
+describe('ContributionForecast', () => {
+  // Helper for generating sequential active days
+  const generateMockActivity = (counts: number[], startYear = 2026): ActivityData[] => {
+    return counts.map((count, index) => {
+      // pad with leading zero
+      const dayStr = String(index + 1).padStart(2, '0');
+      return {
+        date: `${startYear}-06-${dayStr}`,
+        count,
+        intensity: count > 0 ? 3 : 0,
+      };
+    });
+  };
+
+  it('renders forecast headers and elements', () => {
+    const activity = generateMockActivity([1, 2, 3]);
+    render(<ContributionForecast activity={activity} />);
+
+    expect(screen.getByRole('heading', { name: /Contribution Forecast/i })).toBeDefined();
+    expect(screen.getByText(/Predict future growth/i)).toBeDefined();
+  });
+
+  it('calculates average weekly and monthly velocities correctly', () => {
+    // 7 days, 2 commits each day
+    // total commits = 14. avg daily = 2. weekly = 14. monthly = 60.
+    const activity = generateMockActivity([2, 2, 2, 2, 2, 2, 2]);
+    render(<ContributionForecast activity={activity} />);
+
+    expect(screen.getByText('14.0 Commits/Week')).toBeDefined();
+    expect(screen.getByText('60.0 Commits/Month')).toBeDefined();
+  });
+
+  it('handles empty activity data gracefully', () => {
+    render(<ContributionForecast activity={[]} />);
+
+    expect(screen.getByText(/No past activity data available to generate predictions/i)).toBeDefined();
+    expect(screen.queryByText('commits/wk')).toBeNull();
+  });
+
+  it('handles zero-commit activity history correctly', () => {
+    const activity = generateMockActivity([0, 0, 0, 0, 0]);
+    render(<ContributionForecast activity={activity} totalContributions={100} />);
+
+    expect(screen.getByText('0.0 Commits/Week')).toBeDefined();
+    expect(screen.getByText('0.0 Commits/Month')).toBeDefined();
+    expect(screen.getByText('Inactive')).toBeDefined();
+    expect(screen.getByText('Stable Rhythm')).toBeDefined();
+
+    // Projections should equal currentTotal contributions (100) because slope and intercept are 0
+    const projectedCommits = screen.getAllByText('100 Commits');
+    expect(projectedCommits.length).toBeGreaterThanOrEqual(2);
+  });
+
+  it('correctly projects month-end and year-end contributions with linear regression', () => {
+    // Let's create an increasing activity
+    // counts: 1 to 10. last entry: 2026-06-10.
+    // N = 10, meanX = 4.5, meanY = 5.5, slope = 1, intercept = 1
+    // End of June (2026-06-30). Days remaining: 20 days.
+    // Projected daily commits for days 11 to 30:
+    // y_t = t + 1 (since slope=1, intercept=1).
+    // For t = 10 to 29 (day index, where day 1 is index 0, day 30 is index 29):
+    // index for future day is N - 1 + d = 9 + d.
+    // y_t = (9 + d) * 1 + 1 = 10 + d.
+    // For d = 1 to 20: 11 + 12 + ... + 30 = 410.
+    // Current total in activity = 55.
+    // Projected month end total = 55 + 410 = 465.
+    const counts = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+    const activity = generateMockActivity(counts);
+
+    render(<ContributionForecast activity={activity} />);
+
+    // Since totalContributions is not specified, it falls back to sum of activity counts (55).
+    // Month-End target should show 465 commits.
+    expect(screen.getByText('465 Commits')).toBeDefined();
+  });
+
+  it('determines consistency rating and trend categories correctly', () => {
+    // 10 days, 9 active days -> active ratio = 90% -> Elite consistency
+    const activity = generateMockActivity([1, 2, 3, 0, 4, 5, 6, 7, 8, 9]);
+    render(<ContributionForecast activity={activity} />);
+
+    expect(screen.getByText('Elite (Very Consistent)')).toBeDefined();
+    expect(screen.getByText('90% active days')).toBeDefined();
+
+    // slope is positive and strong
+    expect(screen.getByText('Strong Growth')).toBeDefined();
+  });
+});