Lesson 06 — Math and string/array helpers for QA automation

Title: Rounding, Bounds, Random Data, String Search, and Queue Operations

Description: Built-in JavaScript methods are used for common test tasks like rounding numbers, finding minimum and maximum values, generating random test data, normalizing strings, splitting text into tokens, and working with arrays as simple queues or stacks. This includes methods like Math.ceil, Math.floor, Math.min, Math.max, string methods like toLowerCase() and trim(), and array operations like push, pop, shift, and unshift.

Why it matters for QA: Test assertions often depend on calculations like SLA limits, checking text inside logs or error messages, working with lists of values (like selectors or tokens), and simulating queues. Using built-in methods correctly helps avoid extra dependencies and keeps test code simple and reliable.

1. Powers and roots

Prefer ** for integer powers; Math.pow still appears in older codebases.

console.log(2 ** 10); // 1024
console.log(Math.pow(3, 3)); // 27

console.log(Math.sqrt(49)); // 7

2. Rounding: round, ceil, floor, and toFixed

let ms = 87.6;
console.log(Math.round(ms)); // 88
console.log(Math.ceil(ms));  // 88
console.log(Math.floor(ms)); // 87

let ratio = 0.333333;
console.log(ratio.toFixed(2)); // "0.33" — string, not number
console.log(Number(ratio.toFixed(2))); // 0.33

Treat toFixed as string formatting suitable for tolerant display assertions;

3. Math.max and Math.min

let durations = [120, 340, 90, 410];
console.log(Math.max(...durations)); // 410
console.log(Math.min(...durations)); // 90

console.log(Math.max(5, 2, 9)); // 9

4. Math.random

Returns [0, 1).

let suffix = Math.floor(Math.random() * 10_000);
console.log("run-" + suffix);

// random index in array
let tags = ["smoke", "api", "ui"];
let pick = tags[Math.floor(Math.random() * tags.length)];
console.log(pick);

Note: Math.random is not CSPRNG-grade—adequate for test entropy only; never for secrets, signing material, or credential derivation.

5. String case

let env = "StAgInG";
console.log(env.toLowerCase()); // "staging"
console.log(env.toUpperCase()); // "STAGING"

Useful before comparing user input or headers case-insensitively.

6. slice (substring by index)

Does not mutate the string. End index is exclusive.

let url = "https://api.example.com/v2/items";
console.log(url.slice(0, 5));   // "https"
console.log(url.slice(-5));     // "items"

7. Search helpers

let msg = "AssertionError: locator not visible";
console.log(msg.includes("visible"));     // true
console.log(msg.startsWith("Assert"));    // true
console.log(msg.endsWith("visible"));     // true
console.log(msg.indexOf("locator"));      // index or -1

8. split and join

let csv = "one,two,three";
let parts = csv.split(",");
console.log(parts);

let joined = ["2026", "05", "03"].join("-");
console.log(joined); // "2026-05-03"

9. Array ends: push, pop, shift, unshift

All mutate the array in place.

let queue = [];
queue.push("first", "second");
console.log(queue.pop());   // "second" — from end
queue.push("third");
console.log(queue.shift()); // "first" — from start

queue.unshift("priority");
console.log(queue); // ["priority", "third"]

Official docs

• MDN — Math
• MDN — String methods
• MDN — Array methods

Quick recap

Suggested exercises

1. Given let latency = 149.9, store SLA breach as boolean: latency > 100 after rounding up to whole ms.
2. Parse "GET /api/orders HTTP/1.1" into method and path using split.

Homework

Short tasks (about 10–15 minutes). Click a task title to reveal the prompt.