public void AddHeader()
{
GetRequestBuilder <int, Greeting> b = new GetRequestBuilder <int, Greeting>(baseUrl);
b.AddHeader("header1", "value1");
b.AddHeader("header2", "value2");
b.AddHeader("header2", "value22");
CollectionAssert.AreEqual(new List <string>()
{
"value1"
}, b.GetHeader("header1"));
CollectionAssert.AreEqual(new List <string>()
{
"value2", "value22"
}, b.GetHeader("header2"));
}