Pengujian Lanjut: Teknik & Automasi

# ================================================================
# FILE: kalkulator_diskon.py
# Sistem perhitungan diskon e-commerce "TokoKita"
# ================================================================

class KalkulatorDiskon:
    """Menghitung harga akhir setelah diskon."""

    BATAS_DISKON_MEMBER  = 500_000   # Rp 500.000
    DISKON_PREMIUM_BESAR = 0.30      # 30%
    DISKON_PREMIUM_KECIL = 0.15      # 15%
    DISKON_REGULER       = 0.10      # 10%

    def hitung_diskon(self, total_belanja, is_premium, kode_voucher=None):
        """
        Hitung diskon berdasarkan status member dan total belanja.
        Returns: (harga_final, persen_diskon, alasan)
        """
        if total_belanja < 0:
            raise ValueError("Total belanja tidak boleh negatif")

        if kode_voucher == "HEMAT20":
            diskon = 0.20
            alasan = "Voucher HEMAT20 (20%)"
        elif is_premium and total_belanja >= self.BATAS_DISKON_MEMBER:
            diskon = self.DISKON_PREMIUM_BESAR
            alasan = "Member Premium + Belanja ≥ 500rb (30%)"
        elif is_premium:
            diskon = self.DISKON_PREMIUM_KECIL
            alasan = "Member Premium (15%)"
        elif total_belanja >= self.BATAS_DISKON_MEMBER:
            diskon = self.DISKON_REGULER
            alasan = "Belanja ≥ 500rb (10%)"
        else:
            diskon = 0
            alasan = "Tidak ada diskon"

        harga_final = total_belanja * (1 - diskon)
        return harga_final, diskon, alasan

# ================================================================
# FILE: test_kalkulator_diskon.py
# Unit Tests menggunakan pytest
# Teknik: Equivalence Partitioning + Boundary Value Analysis
# Dosen: Riadi Marta Dinata, S.Ti., M.Kom. | ISTN Jakarta
# ================================================================

import pytest
from kalkulator_diskon import KalkulatorDiskon

@pytest.fixture
def kalkulator():
    """Fixture: buat instance KalkulatorDiskon sebelum setiap test."""
    return KalkulatorDiskon()

# ── KELAS 1: Member Premium + Belanja Besar ──
class TestMemberPremiumBelanjaБesar:

    def test_diskon_30_persen_normal(self, kalkulator):
        """TC-01: Premium + total 600rb → diskon 30%"""
        final, diskon, _ = kalkulator.hitung_diskon(600_000, is_premium=True)
        assert diskon == 0.30
        assert final == pytest.approx(420_000)

    def test_boundary_tepat_500rb(self, kalkulator):
        """TC-02: BVA — tepat di boundary 500rb → dapat 30%"""
        final, diskon, _ = kalkulator.hitung_diskon(500_000, is_premium=True)
        assert diskon == 0.30, "Tepat 500rb harus dapat diskon 30%"

    def test_boundary_499rb_premium(self, kalkulator):
        """TC-03: BVA — satu di bawah boundary (499.999) → 15%"""
        _, diskon, _ = kalkulator.hitung_diskon(499_999, is_premium=True)
        assert diskon == 0.15, "499.999 hanya dapat diskon 15%"

# ── KELAS 2: Member Premium + Belanja Kecil ──
class TestMemberPremiumBelanjaKecil:

    def test_diskon_15_persen(self, kalkulator):
        """TC-04: Premium + total 200rb → diskon 15%"""
        final, diskon, _ = kalkulator.hitung_diskon(200_000, is_premium=True)
        assert diskon == 0.15
        assert final == pytest.approx(170_000)

# ── KELAS 3: Reguler + Belanja Besar ──
class TestRegulerBelanjaБesar:

    def test_diskon_10_persen(self, kalkulator):
        """TC-05: Reguler + 700rb → diskon 10%"""
        final, diskon, _ = kalkulator.hitung_diskon(700_000, is_premium=False)
        assert diskon == 0.10
        assert final == pytest.approx(630_000)

# ── KELAS 4: Tanpa Diskon ──
class TestTanpaDiskon:

    def test_no_discount_reguler_kecil(self, kalkulator):
        """TC-06: Reguler + 100rb → tidak ada diskon"""
        final, diskon, alasan = kalkulator.hitung_diskon(100_000, is_premium=False)
        assert diskon == 0
        assert final == 100_000
        assert "Tidak ada" in alasan

# ── KELAS 5: Voucher ──
class TestVoucher:

    def test_voucher_hemat20(self, kalkulator):
        """TC-07: Voucher HEMAT20 → prioritas di atas status member"""
        _, diskon, alasan = kalkulator.hitung_diskon(
            300_000, is_premium=True, kode_voucher="HEMAT20")
        assert diskon == 0.20
        assert "HEMAT20" in alasan

    def test_voucher_invalid(self, kalkulator):
        """TC-08: Voucher tidak valid → diabaikan"""
        _, diskon, _ = kalkulator.hitung_diskon(
            100_000, is_premium=False, kode_voucher="SALAH999")
        assert diskon == 0

# ── KELAS 6: Error Handling ──
class TestErrorHandling:

    def test_total_negatif_raises_error(self, kalkulator):
        """TC-09: Input negatif → harus raise ValueError"""
        with pytest.raises(ValueError, match="tidak boleh negatif"):
            kalkulator.hitung_diskon(-100_000, is_premium=True)

    def test_total_nol(self, kalkulator):
        """TC-10: BVA — total = 0 → valid, tanpa diskon"""
        final, diskon, _ = kalkulator.hitung_diskon(0, is_premium=False)
        assert final == 0
        assert diskon == 0

# ── PARAMETRIZED TEST (Data-Driven) ──
@pytest.mark.parametrize("total,premium,expected_disc", [
    (1_000_000, True,  0.30),  # Premium + besar
    (200_000,   True,  0.15),  # Premium + kecil
    (750_000,   False, 0.10),  # Reguler + besar
    (50_000,    False, 0   ),  # Reguler + kecil
    (500_000,   True,  0.30),  # BVA: tepat boundary
    (499_999,   True,  0.15),  # BVA: satu di bawah
])
def test_parametrized_diskon(kalkulator, total, premium, expected_disc):
    """TC Data-Driven: otomatis menguji 6 kombinasi sekaligus"""
    _, diskon, _ = kalkulator.hitung_diskon(total, is_premium=premium)
    assert diskon == expected_disc