public void FromConfiguration_HttpClientIsNull_ThrowsArgumentNullException()
        {
            var exception = Assert.Throws <ArgumentNullException>(() => HttpClientExtensions.FromConfiguration(null, null, ""));

            Assert.Equal("client", exception.ParamName);

            exception = Assert.Throws <ArgumentNullException>(() => HttpClientExtensions.FromConfiguration(null, "", null));
            Assert.Equal("client", exception.ParamName);
        }