Testing Strategies

A unit test (xUnit, from Level 2) verifies one class in isolation; an integration test verifies several real pieces working together, often against ASP.NET Core's WebApplicationFactory to spin up the whole app in-process for the test.

public class OrderServiceTests {
    [Fact]
    public void AppliesDiscountForLargeOrders() {
        var emailSenderMock = new Mock<IEmailSender>(); // Moq — a mocking library
        var service = new OrderService(emailSenderMock.Object);

        double total = service.CalculateTotal(150.0);

        Assert.Equal(135.0, total); // 10% off orders over 100
    }
}

Moq stands in for a real dependency the same way Mockito does in Java, letting OrderService's own logic be tested without a real email provider.