Create a type for FixedHeader and also a parser.  Replace the usage in the test for the message type to use the FixedHeaderParser
Replace the usage in the test for the duplicate delivery to use the FixedHeaderParser
Replace the usage in the test for the quality of service to use the FixedHeaderParser
Replace the usage in the test for the retain to use the FixedHeaderParser
Replaced the usages in the tests for duplicate delivery and retain
Used the FixedHeaderParser in the quality of service testsecho mocha test/something.js && mocha test/something.js
Used the FixedHeaderParser in the message type tests