public async Task PostsToTheCorrectUrl() { var connection = Substitute.For <IApiConnection>(); var client = new ProductsClient(connection); await client.AddFollower(123, 1234); Received.InOrder(async() => { await connection.Post <ProductFollower>(Arg.Is <Uri>(u => u.ToString() == "products/123/followers"), Arg.Is <object>(o => o.ToString() == new { user_id = 1234 }.ToString())); }); }