budget/BudgetApp.Tests/Domain/MoneyTests.cs

namespace BudgetApp.Tests.Domain;

using BudgetApp.Domain.Models;
using Xunit;

public class MoneyTests
{
    [Fact]
    public void Constructor_WithValidAmount_CreatesMoney()
    {
        // Arrange & Act
        var money = new Money(100.50m, "USD");

        // Assert
        Assert.Equal(100.50m, money.Amount);
        Assert.Equal("USD", money.Currency);
    }

    [Fact]
    public void Constructor_WithNegativeAmount_ThrowsException()
    {
        // Arrange, Act & Assert
        Assert.Throws<ArgumentException>(() => new Money(-100m, "USD"));
    }

    [Fact]
    public void Constructor_WithNullCurrency_ThrowsException()
    {
        // Arrange, Act & Assert
        Assert.Throws<ArgumentException>(() => new Money(100m, null!));
        Assert.Throws<ArgumentException>(() => new Money(100m, ""));
    }

    [Fact]
    public void Add_WithSameCurrency_ReturnsSum()
    {
        // Arrange
        var money1 = new Money(100m, "USD");
        var money2 = new Money(50m, "USD");

        // Act
        var result = money1.Add(money2);

        // Assert
        Assert.Equal(150m, result.Amount);
        Assert.Equal("USD", result.Currency);
    }

    [Fact]
    public void Add_WithDifferentCurrencies_ThrowsException()
    {
        // Arrange
        var money1 = new Money(100m, "USD");
        var money2 = new Money(50m, "EUR");

        // Act & Assert
        Assert.Throws<InvalidOperationException>(() => money1.Add(money2));
    }

    [Fact]
    public void Subtract_WithSameCurrency_ReturnsDifference()
    {
        // Arrange
        var money1 = new Money(100m, "USD");
        var money2 = new Money(50m, "USD");

        // Act
        var result = money1.Subtract(money2);

        // Assert
        Assert.Equal(50m, result.Amount);
    }

    [Fact]
    public void Subtract_ResultingInNegative_ThrowsException()
    {
        // Arrange
        var money1 = new Money(50m, "USD");
        var money2 = new Money(100m, "USD");

        // Act & Assert
        Assert.Throws<InvalidOperationException>(() => money1.Subtract(money2));
    }

    [Fact]
    public void Equals_WithSameAmountAndCurrency_ReturnsTrue()
    {
        // Arrange
        var money1 = new Money(100m, "USD");
        var money2 = new Money(100m, "USD");

        // Act & Assert
        Assert.True(money1.Equals(money2));
        Assert.True(money1 == money2);
    }

    [Fact]
    public void Equals_WithDifferentAmount_ReturnsFalse()
    {
        // Arrange
        var money1 = new Money(100m, "USD");
        var money2 = new Money(50m, "USD");

        // Act & Assert
        Assert.False(money1.Equals(money2));
        Assert.True(money1 != money2);
    }

    [Fact]
    public void OperatorAdd_WithSameCurrency_ReturnsSum()
    {
        // Arrange
        var money1 = new Money(100m, "USD");
        var money2 = new Money(50m, "USD");

        // Act
        var result = money1 + money2;

        // Assert
        Assert.Equal(150m, result.Amount);
    }
}