test: add unit tests for team generation algorithms

Add comprehensive tests for team generation:
- Test random pairing strategy
- Test ELO-based pairing strategy
- Test even matches strategy
- Test minimize repeat partnerships
- Test bye player handling
- Test team balance calculation
- Test partnership frequency tracking

All 19 tests pass.

Refs #22

src/__tests__/unit/team-generator.test.ts

@@ -0,0 +1,281 @@
+/**
+ * Unit Tests: Team Generation Algorithms
+ *
+ * Tests the correctness of team generation algorithms
+ * for different partner rotation strategies.
+ */
+
+import { describe, test, expect } from 'bun:test';
+import {
+  generateTeams,
+  generateRandomTeams,
+  generateEvenTeams,
+  generateELOBasedTeams,
+  calculateTeamBalance,
+  calculatePartnershipFrequency,
+  generateTeamsWithRotation,
+  type Player,
+  type Team,
+  type PartnerRotation,
+} from '@/lib/team-generator';
+
+// Test players with varying ELO ratings
+const testPlayers: Player[] = [
+  { id: 1, name: 'Alice', currentElo: 1500 },
+  { id: 2, name: 'Bob', currentElo: 1200 },
+  { id: 3, name: 'Charlie', currentElo: 1400 },
+  { id: 4, name: 'Diana', currentElo: 1300 },
+  { id: 5, name: 'Eve', currentElo: 1100 },
+  { id: 6, name: 'Frank', currentElo: 1600 },
+];
+
+describe('Team Generation Algorithms', () => {
+  describe('generateTeams', () => {
+    test('should return empty teams for fewer than 2 players', () => {
+      const result = generateTeams([], 'none', true);
+      expect(result.teams).toEqual([]);
+      expect(result.byePlayer).toBeNull();
+    });
+
+    test('should generate one team for 2 players', () => {
+      const players = testPlayers.slice(0, 2);
+      const result = generateTeams(players, 'none', true);
+      expect(result.teams).toHaveLength(1);
+      expect(result.teams[0].player1Id).toBeDefined();
+      expect(result.teams[0].player2Id).toBeDefined();
+    });
+
+    test('should generate correct number of teams for even player count', () => {
+      const players = testPlayers.slice(0, 6);
+      const result = generateTeams(players, 'none', true);
+      expect(result.teams).toHaveLength(3);
+    });
+
+    test('should handle odd player count with byes enabled', () => {
+      const players = testPlayers.slice(0, 5);
+      const result = generateTeams(players, 'none', true);
+      expect(result.teams).toHaveLength(2);
+      expect(result.byePlayer).not.toBeNull();
+      // Bye goes to highest ELO player (player 1 with Elo 1500)
+      expect(result.byePlayer?.id).toBe(1);
+    });
+
+    test('should throw error for odd player count with byes disabled', () => {
+      const players = testPlayers.slice(0, 5);
+      expect(() => generateTeams(players, 'none', false)).toThrow(
+        "Odd number of participants. Enable 'Allow Byes' to proceed."
+      );
+    });
+
+    test('should use different strategies correctly', () => {
+      const players = testPlayers.slice(0, 6);
+      
+      // Test each strategy
+      const strategies: PartnerRotation[] = ['none', 'minimize_repeat', 'maximize_even', 'elo_based'];
+      
+      for (const strategy of strategies) {
+        const result = generateTeams(players, strategy, true);
+        expect(result.teams).toHaveLength(3);
+        expect(result.strategy).toBe(strategy);
+      }
+    });
+  });
+
+  describe('generateRandomTeams', () => {
+    test('should generate all teams with unique players', () => {
+      const players = testPlayers.slice(0, 6);
+      const teams = generateRandomTeams(players);
+      
+      expect(teams).toHaveLength(3);
+      
+      // Collect all player IDs
+      const allPlayerIds = teams.flatMap(t => [t.player1Id, t.player2Id]);
+      const uniqueIds = new Set(allPlayerIds);
+      
+      expect(uniqueIds.size).toBe(6);
+    });
+
+    test('should not create duplicate teams', () => {
+      const players = testPlayers.slice(0, 6);
+      const teams = generateRandomTeams(players);
+      
+      // Check that no team has the same pair
+      const teamKeys = teams.map(t => [t.player1Id, t.player2Id].sort().join('-'));
+      const uniqueKeys = new Set(teamKeys);
+      
+      expect(uniqueKeys.size).toBe(teams.length);
+    });
+
+    test('should include team names', () => {
+      const players = testPlayers.slice(0, 4);
+      const teams = generateRandomTeams(players);
+      
+      for (const team of teams) {
+        expect(team.teamName).toContain('&');
+      }
+    });
+  });
+
+  describe('generateEvenTeams', () => {
+    test('should pair top players with bottom players', () => {
+      const players = testPlayers.slice(0, 6);
+      const teams = generateEvenTeams(players);
+      
+      expect(teams).toHaveLength(3);
+      
+      // Check that teams are balanced
+      const playerMap = new Map(players.map(p => [p.id, p]));
+      let totalDiff = 0;
+      
+      for (const team of teams) {
+        const player1 = playerMap.get(team.player1Id)!;
+        const player2 = playerMap.get(team.player2Id)!;
+        totalDiff += Math.abs(player1.currentElo - player2.currentElo);
+      }
+      
+      // Average difference should be reasonable
+      const avgDiff = totalDiff / teams.length;
+      expect(avgDiff).toBeLessThan(500); // Should be reasonably balanced
+    });
+
+    test('should handle odd number of players', () => {
+      const players = testPlayers.slice(0, 5);
+      const teams = generateEvenTeams(players);
+      
+      expect(teams).toHaveLength(2);
+    });
+  });
+
+  describe('generateELOBasedTeams', () => {
+    test('should pair strongest with weakest', () => {
+      const players = testPlayers.slice(0, 6);
+      const teams = generateELOBasedTeams(players);
+      
+      expect(teams).toHaveLength(3);
+      
+      // Check pairing pattern
+      const sorted = [...players].sort((a, b) => b.currentElo - a.currentElo);
+      
+      for (let i = 0; i < teams.length; i++) {
+        const team = teams[i];
+        const expectedPlayer1 = sorted[i];
+        const expectedPlayer2 = sorted[sorted.length - 1 - i];
+        
+        expect(team.player1Id).toBe(expectedPlayer1.id);
+        expect(team.player2Id).toBe(expectedPlayer2.id);
+      }
+    });
+
+    test('should create balanced teams', () => {
+      const players = testPlayers.slice(0, 6);
+      const teams = generateELOBasedTeams(players);
+      
+      const playerMap = new Map(players.map(p => [p.id, p]));
+      let totalDiff = 0;
+      
+      for (const team of teams) {
+        const player1 = playerMap.get(team.player1Id)!;
+        const player2 = playerMap.get(team.player2Id)!;
+        totalDiff += Math.abs(player1.currentElo - player2.currentElo);
+      }
+      
+      // Average difference should be high for ELO-based pairing
+      const avgDiff = totalDiff / teams.length;
+      expect(avgDiff).toBeGreaterThan(200);
+    });
+  });
+
+  describe('calculateTeamBalance', () => {
+    test('should calculate balance for well-balanced teams', () => {
+      const teams: Team[] = [
+        { player1Id: 1, player2Id: 2, teamName: 'Test' },
+        { player1Id: 3, player2Id: 4, teamName: 'Test' },
+      ];
+      
+      const balance = calculateTeamBalance(teams, testPlayers);
+      expect(balance).toBeGreaterThan(0);
+    });
+
+    test('should return 0 for empty teams', () => {
+      const balance = calculateTeamBalance([], testPlayers);
+      expect(balance).toBe(0);
+    });
+  });
+
+  describe('calculatePartnershipFrequency', () => {
+    test('should count partnerships correctly', () => {
+      const team1: Team[] = [
+        { player1Id: 1, player2Id: 2, teamName: 'Test' },
+        { player1Id: 3, player2Id: 4, teamName: 'Test' },
+      ];
+      
+      const team2: Team[] = [
+        { player1Id: 1, player2Id: 3, teamName: 'Test' },
+        { player1Id: 2, player2Id: 4, teamName: 'Test' },
+      ];
+      
+      const frequency = calculatePartnershipFrequency([team1, team2], testPlayers);
+      
+      expect(frequency.get('1-2')).toBe(1);
+      expect(frequency.get('3-4')).toBe(1);
+      expect(frequency.get('1-3')).toBe(1);
+      expect(frequency.get('2-4')).toBe(1);
+    });
+
+    test('should handle empty previous teams', () => {
+      const frequency = calculatePartnershipFrequency([], testPlayers);
+      expect(frequency.size).toBe(0);
+    });
+  });
+
+  describe('generateTeamsWithRotation', () => {
+    test('should minimize repeat partnerships', () => {
+      const players = testPlayers.slice(0, 6);
+      
+      // First round
+      const firstRound = generateTeams(players, 'none', true);
+      
+      // Second round with rotation
+      const secondRound = generateTeamsWithRotation(
+        players,
+        [firstRound.teams],
+        'minimize_repeat',
+        true
+      );
+      
+      // Check that partnerships are different
+      const firstRoundKeys = new Set(
+        firstRound.teams.map(t => [t.player1Id, t.player2Id].sort().join('-'))
+      );
+      
+      for (const team of secondRound.teams) {
+        const key = [team.player1Id, team.player2Id].sort().join('-');
+        expect(firstRoundKeys.has(key)).toBe(false);
+      }
+    });
+
+    test('should handle multiple previous rounds', () => {
+      const players = testPlayers.slice(0, 6);
+      
+      // Simulate 3 rounds
+      const previousTeams: Team[][] = [];
+      
+      for (let i = 0; i < 3; i++) {
+        const result = generateTeamsWithRotation(
+          players,
+          previousTeams,
+          'minimize_repeat',
+          true
+        );
+        previousTeams.push(result.teams);
+      }
+      
+      expect(previousTeams).toHaveLength(3);
+      
+      // Each round should have 3 teams
+      for (const teams of previousTeams) {
+        expect(teams).toHaveLength(3);
+      }
+    });
+  });
+});