add tests for predictDraw to mirror python

src/__tests__/predict-draw.test.ts

@@ -91,4 +91,33 @@ describe('predictDraw', () => {
       ).toBeCloseTo(0.11489223845523855, 7)
     })
   })
+
+  it('mirrors results from python', () => {
+    // from https://github.com/philihp/openskill.js/issues/599
+    const t1 = [rating({ mu: 25, sigma: 1 }), rating({ mu: 25, sigma: 1 })]
+    const t2 = [rating({ mu: 25, sigma: 1 }), rating({ mu: 25, sigma: 1 })]
+    expect(predictDraw([t1, t2])).toBeCloseTo(0.6608263448857606)
+  })
+
+  it('gives a low probability in a 5 team match', () => {
+    // from https://openskill.me/en/stable/manual.html
+    const p1 = rating({ mu: 35, sigma: 1.0 })
+    const p2 = rating({ mu: 35, sigma: 1.0 })
+    const p3 = rating({ mu: 35, sigma: 1.0 })
+    const p4 = rating({ mu: 35, sigma: 1.0 })
+    const p5 = rating({ mu: 35, sigma: 1.0 })
+
+    const team1 = [p1, p2]
+    const team2 = [p3, p4, p5]
+    expect(predictDraw([team1, team2])).toBeCloseTo(0.0002807397636509501, 10)
+  })
+
+  it('gives a higher probability with fewer players', () => {
+    // from https://openskill.me/en/stable/manual.html
+    const p1 = rating({ mu: 35, sigma: 1.0 })
+    const p2 = rating({ mu: 35, sigma: 1.1 })
+    const team1 = [p1]
+    const team2 = [p2]
+    expect(predictDraw([team1, team2])).toBeCloseTo(0.4868868769871696)
+  })
 })