Test.cs

public class Tests
{
    [Fact]
    public async Task Test()
    {
      var mock = new Mock<IVinDecoderService>();

      mock.Setup(x => x.Lookup("123456789"))
        .ReturnsAsync(new VinDecoderResult
        {
            Make = "Ford",
            Model = "F-150",
            Year = 2026
        });

        var sut = new RegisterVehicleHandler(mock.Object);
        var result = await sut.Handle(new RegisterVehicle("123456789"), CancellationToken.None);

        Assert.Equal("2026 Ford F-150", result);
    }
}