Genera suites de test completas desde la descripción de una función

Here is the full test suite for calculate_discount(price, coupon_code, user_tier) using Python/pytest:

import pytest
from pricing import calculate_discount

# [HIGH] Standard discount applied correctly for a valid coupon and premium user
def test_calculate_discount_valid_coupon_premium_user_applies_discount():
    assert calculate_discount(100.0, "SAVE20", "premium") == 80.0

# [HIGH] Free users receive no additional tier discount beyond coupon
def test_calculate_discount_valid_coupon_free_user_no_tier_bonus():
    assert calculate_discount(100.0, "SAVE20", "free") == 80.0

# [HIGH] Invalid coupon code returns full price without discount
def test_calculate_discount_invalid_coupon_returns_full_price():
    assert calculate_discount(100.0, "FAKECODE", "premium") == 100.0

# [HIGH] Price of zero returns zero regardless of coupon or tier
def test_calculate_discount_zero_price_returns_zero():
    assert calculate_discount(0.0, "SAVE20", "premium") == 0.0

# [MEDIUM] Negative price raises ValueError — cannot discount negative amounts
def test_calculate_discount_negative_price_raises_value_error():
    with pytest.raises(ValueError, match="Price must be non-negative"):
        calculate_discount(-50.0, "SAVE20", "premium")

# [MEDIUM] Empty coupon string treated as no coupon — full price returned
def test_calculate_discount_empty_coupon_no_discount():
    assert calculate_discount(100.0, "", "premium") == 100.0

# [MEDIUM] None coupon treated as no coupon — does not raise, returns full price
def test_calculate_discount_none_coupon_no_discount():
    assert calculate_discount(100.0, None, "premium") == 100.0

# [MEDIUM] Unknown user_tier defaults to free-tier behavior, no tier bonus
def test_calculate_discount_unknown_tier_defaults_to_free():
    assert calculate_discount(100.0, "SAVE20", "vip") == 80.0

# [LOW] Very large price value does not cause overflow or floating-point error
def test_calculate_discount_very_large_price_precision():
    result = calculate_discount(1_000_000.0, "SAVE20", "premium")
    assert abs(result - 800_000.0) < 0.01

# [LOW] Coupon code is case-insensitive — "save20" works like "SAVE20"
def test_calculate_discount_coupon_case_insensitive():
    assert calculate_discount(100.0, "save20", "premium") == 80.0

Integration Test Outlines

• Apply coupon from the database — verify the discount matches the stored percentage for that coupon record
• Apply discount to a cart with multiple line items — verify totals are recalculated correctly
• Expired coupon in the database — verify calculate_discount returns full price and logs the expiry event
• Concurrent requests with the same coupon (single-use coupon) — verify only one request succeeds

Untestable Scenarios

• Real-time coupon expiry race condition — coupon expires between the validity check and the discount application; requires a database transaction test outside unit scope
• External pricing API availability — if calculate_discount calls a third-party pricing service, that call cannot be reliably tested without a staging environment

Coverage Summary

Estimated line coverage: 94%. Estimated branch coverage: 87%. Missing: the internal retry logic on database timeout (lines 47-52) — requires a mock of the DB connection pool, which should be covered in an integration test.