public async Task WhenSuccessfullyCreated_ReturnsId(Guid id)
{
// Given
this.repository.CreateCart().Returns(id);
// When
var result = await this.client.PostAsJsonAsync(
"/v1/carts",
default(object));
// Then
AssertExt.ReturnsStatusCode_Created(result);
await AssertExt.ReturnsIdOfCreatedCart(id, result);
}