3.2Lists and Arrays

Lists (Python) and arrays (JavaScript) are the most common data structure in test automation. API responses contain lists of items. Test results are lists of pass/fail records. Log files are lists of lines.

Python Lists

# Filtering test results
results = [
    {"name": "test_login", "status": "PASS", "duration": 1.2},
    {"name": "test_signup", "status": "FAIL", "duration": 3.5},
    {"name": "test_logout", "status": "PASS", "duration": 0.8},
    {"name": "test_profile", "status": "FAIL", "duration": 2.1},
]

# List comprehension: filter failed tests
failed = [t for t in results if t["status"] == "FAIL"]
assert len(failed) == 2

# Sort by duration (slowest first)
slowest = sorted(results, key=lambda t: t["duration"], reverse=True)
assert slowest[0]["name"] == "test_signup"

# Extract just the names
names = [t["name"] for t in results]
assert "test_login" in names

# Check all tests passed (returns False if any failed)
all_passed = all(t["status"] == "PASS" for t in results)
assert not all_passed

# Check at least one test passed
any_passed = any(t["status"] == "PASS" for t in results)
assert any_passed

JavaScript/TypeScript Arrays

const results = [
    { name: "test_login", status: "PASS", duration: 1.2 },
    { name: "test_signup", status: "FAIL", duration: 3.5 },
    { name: "test_logout", status: "PASS", duration: 0.8 },
    { name: "test_profile", status: "FAIL", duration: 2.1 },
];

// Filter failed tests
const failed = results.filter(t => t.status === "FAIL");
expect(failed).toHaveLength(2);

// Sort by duration (slowest first) — note: sort mutates the array
const slowest = [...results].sort((a, b) => b.duration - a.duration);
expect(slowest[0].name).toBe("test_signup");

// Extract just the names
const names = results.map(t => t.name);
expect(names).toContain("test_login");

// Check all/any
const allPassed = results.every(t => t.status === "PASS");
const anyPassed = results.some(t => t.status === "PASS");

Common List Operations in Testing

Operation	Python	JavaScript
Filter	[x for x in list if cond] or filter()	array.filter(fn)
Transform	[fn(x) for x in list] or map()	array.map(fn)
Sort	sorted(list, key=fn)	[...array].sort(fn)
Find first	next((x for x in list if cond), None)	array.find(fn)
Check all	all(cond for x in list)	array.every(fn)
Check any	any(cond for x in list)	array.some(fn)
Flatten	[item for sub in nested for item in sub]	array.flat()
Unique	list(set(list))	[...new Set(array)]