chore(test): add repartition test

packages/core/src/__tests__/repartition.test.ts

@@ -0,0 +1,52 @@
+import { describe, expect, it } from "vitest";
+import { createFlagEngine } from "..";
+
+const engine = createFlagEngine([
+  {
+    key: "summer-sale",
+    status: "enabled",
+    strategies: [
+      {
+        name: "All audience",
+        rules: [],
+        variants: [
+          {
+            name: "A",
+            percent: 50,
+          },
+          {
+            name: "B",
+            percent: 50,
+          },
+        ],
+      },
+    ],
+  },
+]);
+
+describe("repartition", () => {
+  it("should be distributive", () => {
+    const COUNT = 1000_000;
+    let A = 0;
+    let B = 0;
+
+    for (let i = 0; i < COUNT; i++) {
+      const userCtx = engine.createUserContext({ __id: `user-${i}` });
+      const variant = userCtx.evaluate("summer-sale");
+      if (variant === "A") {
+        A++;
+      } else if (variant === "B") {
+        B++;
+      }
+    }
+
+    const halfCount = COUNT / 2;
+    const halfCountUpper = halfCount * 1.01;
+    const halfCountLower = halfCount * 0.99;
+
+    expect(A).toBeGreaterThan(halfCountLower);
+    expect(A).toBeLessThan(halfCountUpper);
+    expect(B).toBeGreaterThan(halfCountLower);
+    expect(B).toBeLessThan(halfCountUpper);
+  });
+});