package com.bookshop.dry;

import static org.junit.jupiter.api.Assertions.assertEquals;

import com.bookshop.domain.Book;
import java.math.BigDecimal;
import java.util.List;
import org.junit.jupiter.api.DisplayName;
import org.junit.jupiter.api.Test;

@DisplayName("DRY -- one authoritative home for the VAT rule, so documents cannot disagree")
class VatDryTest {

    @Test
    @DisplayName("the knowledge itself has exactly one place and one test")
    void vatRuleHasOneHome() {
        assertEquals(new BigDecimal("2.00"), Vat.vatOn(new BigDecimal("10.00")));
        assertEquals(new BigDecimal("12.00"), Vat.withVat(new BigDecimal("10.00")));
    }

    @Test
    @DisplayName("receipt and invoice agree by construction, not by careful copy-paste")
    void documentsCannotDrift() {
        List<Book> basket = List.of(
                new Book("978-0132350884", "Clean Code", "Robert C. Martin", new BigDecimal("32.50")));

        BigDecimal onReceipt = new CustomerReceipt().totalWithVat(basket);
        BigDecimal onInvoice = new SupplierInvoice().grandTotal(new BigDecimal("32.50"));

        assertEquals(onReceipt, onInvoice);
        assertEquals(new BigDecimal("39.00"), onReceipt);
    }
}

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