fix rng

app/src/shared/utils.ts

@@ -11,6 +11,8 @@ export function randomId(): string {
 // rng(1, 5) #=> result can be 1 2 3 4 or 5
 // rng(2)    #=> result can be 1 or 2
 export function rng(min: number, max = 0) {
+    if (min === 0 && max === 0) return 0
+
     if (max === 0) {
         max = min
         min = 1

app/test/rng.test.ts

@@ -0,0 +1,20 @@
+import { test } from "bun:test"
+import { equal as assertEqual, ok as assert } from "assert"
+import { rng, randomIndex } from "../src/shared/utils"
+
+test("randomIndex", () => {
+  let idx = randomIndex([5, 7, 9])!
+  assert(idx >= 0 && idx < 3)
+
+  idx = randomIndex([5])!
+  assertEqual(idx, 0)
+})
+
+test("rng", () => {
+  assertEqual(rng(0, 0), 0)
+
+  const samples = Array.from({ length: 1000 }, () => rng(0, 1))
+  const avg = samples.reduce((a, b) => a + b, 0) / samples.length
+  assert(avg > 0.45 && avg < 0.55, "Average not close to 0.5")
+})
+