private void AssertHeader(IHeader header)
{
var headerObj = JsonObject.Parse(header.JsonString());
var subs = headerObj.Object("sub");
var firstNameSubstitutions = subs.Get<string[]>(FirstNamePlaceholder).ToList();
CollectionAssert.AreEqual(new List<string> { Subscriber1FirstName, Subscriber2FirstName }, firstNameSubstitutions);
var lastNameSubstitutions = subs.Get<string[]>(LastNamePlaceholder).ToList();
CollectionAssert.AreEqual(new List<string> { "", Subscriber2LastName }, lastNameSubstitutions);
var emailSubstitutions = subs.Get<string[]>(EmailPlaceholder).ToList();
CollectionAssert.AreEqual(new List<string> { Subscriber1Email, Subscriber2Email }, emailSubstitutions);
var resolveKeySubstitutions = subs.Get<string[]>(ResolveKeyPlaceholder).ToList();
CollectionAssert.AreEqual(new List<string> { Subscriber1ResolveKey, Subscriber2ResolveKey }, resolveKeySubstitutions);
var uniqueArgs = headerObj.Object("unique_args");
var campaingId = uniqueArgs.Get(CampaignCustomHeaderKey);
Assert.AreEqual(CampaignCustomHeaderValue, campaingId);
var subscriberId = uniqueArgs.Get(SubscriberCustomHeaderKey);
Assert.AreEqual(SubscriberCustomHeaderValue, subscriberId);
}