Kenyan Asbel Kiprop has been given a 4 year ban for doping. Kiprop is the 3rd fastest male 1,500m runner of all-time and many time global champion over the same distance. His story includes admission of monetary payment to a drug tester as well as advanced notice of drug testing, of which there have been other recorded examples, including: olympics.nbcsports.com/2016/03/26/kenya-doping-drug-tests-track-and-field/amp.

On Twitter, Ross Tucker did a good job of walking through the various defenses presented by Kiprop: twitter.com/Scienceofsport/status/1119556982682390529?s=03

Although a lengthy read, it's worthwhile to work through the Decision of the Disciplinary Tribunal to get a sense of how this process works.
www.athleticsintegrity.org/downloads/pdfs/disciplinary-process/en/IAAF-v-Kiprop-Final-Decision.pdf