public async Task Test_CreateAsync_Concrete_Async()
        {
            // Cancellation token.
            CancellationToken cancellationToken = CancellationToken.None;

            // The client factory.
            var factory = new HttpClientFactory();

            // Not null.
            Assert.NotNull(factory);

            // Create client.
            HttpClient client = await factory.CreateAsync(null, true, cancellationToken).ConfigureAwait(false);

            // Not null.
            Assert.NotNull(client);
        }