Best AI Tools for Unit Test Generation

import pytestfrom datetime import datetime, timedeltafrom app.services.billing import calculate_prorated_refund# Claude Code generated this with ZERO prompting beyond the function name# It spotted the edge case: what if refund_date == subscription_start?class TestCalculateProratedRefund:    def test_full_month_no_refund(self):        """No refund when cancelled on the last day"""        result = calculate_prorated_refund(            amount=100.0,            subscription_start=datetime(2024, 1, 1),            refund_date=datetime(2024, 1, 31)        )        assert result == 0.0    def test_half_month_refund(self):        """50% refund for mid-month cancellation"""        result = calculate_prorated_refund(            amount=100.0,            subscription_start=datetime(2024, 1, 1),            refund_date=datetime(2024, 1, 15)        )        assert pytest.approx(result, 0.01) == 48.39    def test_refund_date_equals_start_date(self):        """Edge case: same-day cancellation = full refund"""        result = calculate_prorated_refund(            amount=100.0,            subscription_start=datetime(2024, 1, 1),            refund_date=datetime(2024, 1, 1)        )        assert result == 100.0    def test_zero_amount_raises(self):        """Invalid input: zero amount should raise ValueError"""        with pytest.raises(ValueError, match="Amount must be positive"):            calculate_prorated_refund(                amount=0.0,                subscription_start=datetime(2024, 1, 1),                refund_date=datetime(2024, 1, 15)            )

import { validateEmail } from './validators';// Copilot generated this inline as we typed the function// Strong on happy path, needed prompting for edge casesdescribe('validateEmail', () => {    it('returns true for valid email', () => {        expect(validateEmail('[email protected]')).toBe(true);    });    it('returns false for missing @ symbol', () => {        expect(validateEmail('userexample.com')).toBe(false);    });    it('returns false for empty string', () => {        expect(validateEmail('')).toBe(false);    });    it('returns false for null input', () => {        expect(validateEmail(null)).toBe(false);    });});