feat: refactor project

backend/tests/test_elo.py

@@ -0,0 +1,46 @@
+"""Tests for the ELO calculation module."""
+
+import pytest
+
+from app.elo import calculate_elo
+
+
+class TestCalculateElo:
+    """Tests for calculate_elo."""
+
+    def test_equal_ratings(self):
+        """Equal ratings should produce symmetric changes."""
+        new_w, new_l = calculate_elo(1500.0, 1500.0, k_factor=32.0)
+        assert new_w > 1500.0
+        assert new_l < 1500.0
+        assert new_w - 1500.0 == pytest.approx(1500.0 - new_l, abs=0.01)
+
+    def test_higher_rated_wins(self):
+        """Higher-rated winner should get a small gain."""
+        new_w, new_l = calculate_elo(1800.0, 1200.0, k_factor=32.0)
+        change = new_w - 1800.0
+        assert 0 < change < 16.0  # expected win → small gain
+
+    def test_lower_rated_wins(self):
+        """Lower-rated winner (upset) should get a large gain."""
+        new_w, new_l = calculate_elo(1200.0, 1800.0, k_factor=32.0)
+        change = new_w - 1200.0
+        assert change > 16.0  # upset → large gain
+
+    def test_k_factor_scales_change(self):
+        """Higher K-factor should produce larger rating changes."""
+        _, _ = calculate_elo(1500.0, 1500.0, k_factor=16.0)
+        new_w_16, _ = calculate_elo(1500.0, 1500.0, k_factor=16.0)
+        new_w_64, _ = calculate_elo(1500.0, 1500.0, k_factor=64.0)
+        assert (new_w_64 - 1500.0) > (new_w_16 - 1500.0)
+
+    def test_total_elo_preserved(self):
+        """Total ELO should be preserved (zero-sum)."""
+        new_w, new_l = calculate_elo(1600.0, 1400.0, k_factor=32.0)
+        assert new_w + new_l == pytest.approx(1600.0 + 1400.0, abs=0.01)
+
+    def test_result_is_rounded(self):
+        """Results should be rounded to 2 decimal places."""
+        new_w, new_l = calculate_elo(1500.0, 1500.0, k_factor=32.0)
+        assert new_w == round(new_w, 2)
+        assert new_l == round(new_l, 2)