public void GetHeader_WhenHeaderDoesNotExists_ThrowsException()
{
Dictionary <string, string> mockHeaders = new Dictionary <string, string>();
mockHeaders.Add("Header1", "Value1");
mockHeaders.Add("Header3", "Value3");
HttpClientResponse response = new HttpClientResponse("Content", mockHeaders, true);
Assert.AreEqual("Value1", response.GetHeader("Header1"));
Assert.AreEqual("Value3", response.GetHeader("Header3"));
response.GetHeader("Header2");
}