Exercise baseline

tests/Web.Tests/DtoMapperTests.cs

@@ -0,0 +1,163 @@
+using Domain;
+using static TestData.ClientBuilder;
+using static TestData.OrderBuilder;
+
+namespace Web.Tests;
+
+/// <summary>The hand-written <see cref="DtoMappers"/> map both ways, never mutate their input, and round-trip losslessly; domain objects come from the test-data builders, DTO initializers stay literal.</summary>
+public class DtoMapperTests
+{
+    // (1) Mappers map all scalar fields, in both directions.
+    [Fact]
+    public void ToClientDto_maps_all_scalar_fields()
+    {
+        var id = Guid.NewGuid();
+        var client = ValidClient().WithId(id).WithName("Acme").Build();
+
+        var dto = DtoMappers.ToClientDto(client);
+
+        Assert.Equal(id, dto.Id);
+        Assert.Equal("Acme", dto.Name);
+    }
+
+    [Fact]
+    public void ToOrderDto_maps_all_scalar_fields()
+    {
+        var id = Guid.NewGuid();
+        var order = ValidOrder().WithId(id).WithDescription("one").WithTotal(150_00).Build();
+
+        var dto = DtoMappers.ToOrderDto(order);
+
+        Assert.Equal(id, dto.Id);
+        Assert.Equal("one", dto.Description);
+        Assert.Equal(150_00, dto.TotalInCents);
+    }
+
+    [Fact]
+    public void FromClientDto_maps_all_scalar_fields()
+    {
+        var id = Guid.NewGuid();
+        var dto = new ClientDto { Id = id, Name = "Acme" };
+
+        var client = DtoMappers.FromClientDto(dto);
+
+        Assert.Equal(id, client.Id);
+        Assert.Equal("Acme", client.Name);
+    }
+
+    [Fact]
+    public void FromOrderDto_maps_all_scalar_fields()
+    {
+        var id = Guid.NewGuid();
+        var dto = new OrderDto { Id = id, Description = "one", TotalInCents = 150_00 };
+
+        var order = DtoMappers.FromOrderDto(dto);
+
+        Assert.Equal(id, order.Id);
+        Assert.Equal("one", order.Description);
+        Assert.Equal(150_00, order.TotalInCents);
+    }
+
+    // (2) Mappers map the relations, and the back-references stay consistent.
+    [Fact]
+    public void ToClientDto_maps_orders_and_keeps_the_back_reference_consistent()
+    {
+        var order = ValidOrder().WithDescription("one").Build();
+        var client = ValidClient().WithName("Acme").WithOrder(order).Build();
+
+        var dto = DtoMappers.ToClientDto(client);
+        var orderDto = Assert.Single(dto.Orders);
+
+        // The order is mapped with the client's data:
+        Assert.Equal(order.Id, orderDto.Id);
+        Assert.Equal(order.Description, orderDto.Description);
+
+        // The back-reference cycle is resolved to the SAME dto reference:
+        Assert.Same(dto, orderDto.ClientDto);
+    }
+
+    [Fact]
+    public void FromClientDto_wires_the_order_client_back_reference()
+    {
+        var orderDto = new OrderDto { Description = "one" };
+        var dto = new ClientDto { Name = "Acme", Orders = new[] { orderDto } };
+
+        var client = DtoMappers.FromClientDto(dto);
+        var order = Assert.Single(client.Orders);
+
+        Assert.Equal(orderDto.Description, order.Description);
+        // Navigation fix-up: the reconstructed order points at the client:
+        Assert.Same(client, order.Client);
+    }
+
+    // (3) Round-trips preserve all state (compared by values, not reference).
+    [Fact]
+    public void Domain_round_trip_preserves_all_state()
+    {
+        var order = ValidOrder().WithId(Guid.NewGuid()).WithDescription("one").WithTotal(150_00).Build();
+        var client = ValidClient().WithId(Guid.NewGuid()).WithName("Acme").WithOrder(order).Build();
+
+        var roundTrip = DtoMappers.FromClientDto(DtoMappers.ToClientDto(client));
+
+        Assert.Equal(client.Id, roundTrip.Id);
+        Assert.Equal(client.Name, roundTrip.Name);
+        var roundTripOrder = Assert.Single(roundTrip.Orders);
+        Assert.Equal(order.Id, roundTripOrder.Id);
+        Assert.Equal(order.Description, roundTripOrder.Description);
+        Assert.Equal(order.TotalInCents, roundTripOrder.TotalInCents);
+        // The back-reference is still consistent on the reconstructed graph:
+        Assert.Same(roundTrip, roundTripOrder.Client);
+    }
+
+    [Fact]
+    public void Dto_round_trip_preserves_all_state()
+    {
+        var order = ValidOrder().WithId(Guid.NewGuid()).WithDescription("one").WithTotal(150_00).Build();
+        var client = ValidClient().WithId(Guid.NewGuid()).WithName("Acme").WithOrder(order).Build();
+        var dto = DtoMappers.ToClientDto(client);
+        var dtoOrder = dto.Orders[0];
+
+        var roundTrip = DtoMappers.ToClientDto(DtoMappers.FromClientDto(dto));
+
+        Assert.Equal(dto.Id, roundTrip.Id);
+        Assert.Equal(dto.Name, roundTrip.Name);
+        var roundTripOrder = Assert.Single(roundTrip.Orders);
+        Assert.Equal(dtoOrder.Id, roundTripOrder.Id);
+        Assert.Equal(dtoOrder.Description, roundTripOrder.Description);
+        Assert.Equal(dtoOrder.TotalInCents, roundTripOrder.TotalInCents);
+        Assert.Same(roundTrip, roundTripOrder.ClientDto);
+    }
+
+    // (4) Mappers do not mutate their inputs (snapshot fields, map, compare).
+    [Fact]
+    public void ToClientDto_does_not_mutate_the_domain()
+    {
+        var order = ValidOrder().WithId(Guid.NewGuid()).WithDescription("one").Build();
+        var client = ValidClient().WithId(Guid.NewGuid()).WithName("Acme").WithOrder(order).Build();
+        var ordersCount = client.Orders.Count;
+
+        DtoMappers.ToClientDto(client);
+        DtoMappers.ToOrderDto(order);
+
+        Assert.Equal("Acme", client.Name);
+        Assert.Equal(ordersCount, client.Orders.Count);
+        Assert.Same(client, order.Client);          // back-reference untouched
+        Assert.Equal("one", order.Description);
+    }
+
+    [Fact]
+    public void FromClientDto_does_not_mutate_the_dto()
+    {
+        var orderDto = new OrderDto { Description = "one" };
+        var dto = new ClientDto { Id = Guid.NewGuid(), Name = "Acme", Orders = new[] { orderDto } };
+
+        DtoMappers.FromClientDto(dto);
+        DtoMappers.FromOrderDto(orderDto);
+
+        Assert.Equal("Acme", dto.Name);
+        Assert.Same(orderDto, Assert.Single(dto.Orders));   // collection untouched
+        Assert.Null(orderDto.ClientDto);                   // back-reference untouched
+        Assert.Equal("one", orderDto.Description);
+    }
+
+}