3.4Sets

Sets provide fast membership checks, deduplication, and set operations (union, intersection, difference). They are essential for validating response fields and detecting duplicates.

Python Sets

# Validate required fields in API response
required = {"id", "name", "email", "created_at"}
actual = set(response.json().keys())
missing = required - actual
assert not missing, f"Missing fields: {missing}"

# Check no sensitive fields are exposed
forbidden = {"password", "password_hash", "ssn", "credit_card"}
exposed = forbidden & actual  # intersection
assert not exposed, f"Sensitive fields exposed: {exposed}"

# Detect duplicate IDs across paginated responses
page1_ids = {u["id"] for u in page1_response.json()["items"]}
page2_ids = {u["id"] for u in page2_response.json()["items"]}
overlap = page1_ids & page2_ids
assert not overlap, f"Duplicate IDs across pages: {overlap}"

# Verify all expected statuses are present
expected_statuses = {"pending", "processing", "completed", "failed"}
actual_statuses = {o["status"] for o in orders}
missing_statuses = expected_statuses - actual_statuses
# (This tells you which statuses are not represented in the data)

JavaScript Sets

// Deduplication
const ids = responses.map(r => r.id);
const uniqueIds = new Set(ids);
expect(uniqueIds.size).toBe(ids.length);  // no duplicates

// Field validation
const required = new Set(["id", "name", "email", "created_at"]);
const actual = new Set(Object.keys(response.data));
const missing = [...required].filter(f => !actual.has(f));
expect(missing).toHaveLength(0);

Set Operations Reference

Operation	Python	Use Case
Union	a | b	All fields from two responses combined
Intersection	a & b	Fields present in both responses
Difference	a - b	Fields in a but not in b
Symmetric Diff	a ^ b	Fields in one but not both
Subset check	a <= b	Are all required fields present?