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🧪 Add test coverage for pickRandomEndpoint #542

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🧪 Add test coverage for pickRandomEndpoint #542

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5d09416
🧪 [test] add tests for pickRandomEndpoint
google-labs-jules[bot] Apr 14, 2026
184b18d
🧪 [test] add tests for pickRandomEndpoint
google-labs-jules[bot] Apr 14, 2026
f44ab0a
🧪 [test] add tests for pickRandomEndpoint
google-labs-jules[bot] Apr 14, 2026
bdaf3cd
🧪 [test] add tests for pickRandomEndpoint
google-labs-jules[bot] Apr 14, 2026
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33 changes: 32 additions & 1 deletion src/__tests__/endpoint.test.ts
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
import { describe, expect, mock, test } from 'bun:test';
import { executeEndpointFallback } from '../endpoint';
import { executeEndpointFallback, pickRandomEndpoint } from '../endpoint';

const delay = (ms: number) =>
new Promise<void>(resolve => {
Expand Down Expand Up @@ -90,3 +90,34 @@ describe('executeEndpointFallback', () => {
expect(tryEndpoint.mock.calls.map(call => call[0])).toEqual(['a', 'b', 'c']);
});
});

describe('pickRandomEndpoint', () => {
test('returns undefined for empty arrays', () => {
expect(pickRandomEndpoint([])).toBeUndefined();
});

test('deterministically selects an endpoint using a custom random parameter', () => {
const endpoints = ['a', 'b', 'c'];

// Test random = 0 (picks first)
const endpoints1 = [...endpoints];
expect(pickRandomEndpoint(endpoints1, () => 0)).toBe('a');

// Test random = 0.5 (picks middle)
const endpoints2 = [...endpoints];
expect(pickRandomEndpoint(endpoints2, () => 0.5)).toBe('b');

// Test random = 0.99 (picks last)
const endpoints3 = [...endpoints];
expect(pickRandomEndpoint(endpoints3, () => 0.99)).toBe('c');
});

test('mutates the original array by removing the selected endpoint', () => {
const endpoints = ['a', 'b', 'c'];
const result = pickRandomEndpoint(endpoints, () => 0.5);

expect(result).toBe('b');
expect(endpoints).toEqual(['a', 'c']);
expect(endpoints.length).toBe(2);
});
});
14 changes: 8 additions & 6 deletions src/endpoint.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -44,12 +44,11 @@ export const dedupeEndpoints = (

export const pickRandomEndpoint = (
endpoints: string[],
random: () => number = Math.random,
) => {
if (!endpoints.length) {
throw new Error('No endpoints configured');
}
return endpoints[Math.floor(random() * endpoints.length)];
random = Math.random,
): string | undefined => {
if (endpoints.length === 0) return undefined;
const index = Math.floor(random() * endpoints.length);
return endpoints.splice(index, 1)[0];
Comment on lines 45 to +51
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@coderabbitai coderabbitai bot Apr 14, 2026

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⚠️ Potential issue | 🟡 Minor

Validate the injected RNG output before using it as an index.

random is part of the API here. Values like 1, negatives, or NaN can make splice(index, 1)[0] return the wrong element or undefined, which also makes the non-null assertion at Line 125 unsafe.

Proposed fix 
 export const pickRandomEndpoint = (
   endpoints: string[],
   random = Math.random,
 ): string | undefined => {
   if (endpoints.length === 0) return undefined;
-  const index = Math.floor(random() * endpoints.length);
+  const value = random();
+  if (!Number.isFinite(value) || value < 0 || value >= 1) {
+    throw new RangeError('random() must return a number in [0, 1)');
+  }
+  const index = Math.floor(value * endpoints.length);
   return endpoints.splice(index, 1)[0];
 };
📝 Committable suggestion

‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.

Suggested change
export const pickRandomEndpoint = (
endpoints: string[],
random: () => number = Math.random,
) => {
if (!endpoints.length) {
throw new Error('No endpoints configured');
}
return endpoints[Math.floor(random() * endpoints.length)];
random = Math.random,
): string | undefined => {
if (endpoints.length === 0) return undefined;
const index = Math.floor(random() * endpoints.length);
return endpoints.splice(index, 1)[0];
export const pickRandomEndpoint = (
endpoints: string[],
random = Math.random,
): string | undefined => {
if (endpoints.length === 0) return undefined;
const value = random();
if (!Number.isFinite(value) || value < 0 || value >= 1) {
throw new RangeError('random() must return a number in [0, 1)');
}
const index = Math.floor(value * endpoints.length);
return endpoints.splice(index, 1)[0];
};
🤖 Prompt for AI Agents 
Verify each finding against the current code and only fix it if needed.

In `@src/endpoint.ts` around lines 45 - 51, The RNG output used in
pickRandomEndpoint (params: endpoints, random) must be validated before
computing the splice index: read random() into a value, coerce to Number, verify
it's finite and within [0,1), then compute index = Math.floor(value *
endpoints.length) and clamp to the valid index range (0 .. endpoints.length-1)
to avoid NaN, negatives or >=1 producing out-of-range indices; if validation
fails, fall back to a safe default index (e.g., 0) and then call
endpoints.splice(index, 1)[0] so the returned element is always defined and safe
for downstream non-null usage.

};

export async function selectFastestSuccessfulEndpoint<T>(
Expand Down Expand Up @@ -124,6 +123,9 @@ export async function executeEndpointFallback<T>({
}

const firstEndpoint = pickRandomEndpoint(candidates, random);
if (!firstEndpoint) {
throw new Error('No endpoints configured');
}

try {
return {
Expand Down