Sun sat before sport's highest tribunal to clear his name after the World Anti-Doping Agency (WADA) appealed against him and FINA over its previous decision in favour of Sun on his alleged anti-doping rule violations.
"I am innocent," said Sun, 27. "I believe the panel will make a fair decision and find me innocent."
Sun said: "How can the spirit of fair play be achieved if organisations break their own rules? How can the Olympic dream be fulfilled if the basic rights of athletes are not guaranteed? In order to protect my rights as an athlete, I am determined to fight to the end."
Sun's speech was briefly interrupted when a man suddenly appeared beside the swimmer and tried to replace the translator that Sun clearly was not satisfied with, Xinhua news reports.
The man was persuaded to leave before Sun continued: "It is important to fight against doping, but it is also important that the regulations are complied with by everyone, including the anti-doping organization itself. Otherwise, everyone here behind me now can be the doping officers without training and officially authorized accreditation."
CAS panel president Franco Frattini closed the one-day hearing as he thanked the nine people, including Sun, who testified in only the second public hearing in CAS history.Frattini said he wanted Sun to be "sure of two things that he has the full right to be heard and is completely respected."
Sun refused to complete a doping test conducted by the international testing company IDTM on September 4, 2018, saying the Doping Control Officer (DCO) and her assistants lacked sufficient authorization and credentials.
His case was heard by FINA who decided on January 3 this year that the swimmer was not guilty of anti-doping rule violation. WADA disagreed and appealed the decision.
In the hearing, Sun explained that he stopped cooperating in the process because he found the Doping Control Assistant's behaviour unprofessional.
"He took out his cellphone and started to film me. He said he was a fan of mine and liked me a lot. This was ridiculous. That's why I started to be suspicious," Sun said.
International Doping Tests & Management (IDTM) testing coordinator Tudor Popa said it was the DCO who gives doping control training to his or her assistants.
Popa said they offer the DCOs doping control "education" while the latter "will give training" to their assistants.
Sun said another reason for him to protest was that he didn't see his or their names on relevant documents.
"I only saw FINA's authorisation letter. Although my English is not good enough for me to understand everything on the letter, I did not see my name on it," said Sun.
"Neither did I see names of the three testing personnel on the letter. In my opinion, they should carry with them a clear document with their names on it in order to conduct a test on me," he said.
Sun said he was aware that the DCO was from IDTM because "I made a complaint about the DCO in 2017 when the tester failed to show an authorized document."
Chinese anti-doping expert Han Zhaoqi said that athletes will not refuse to take doping tests if the DCOs have proper credentials.
"Athletes will not refuse to take doping tests as long as they can confirm that the DCOs are authorized and have proper credentials," said Han, a doctor and professor from Zhejiang College of Sports, in the hearing.
"I can't call the vials of blood they took 'doping test samples' because they were taken by people who were not properly credentialed and authorized," said Han.
"I take anti-doping lectures every year at China Anti-Doping Agency (CHINADA). And I know that CHINADA issues DCO credential to each and every DCO in China, and they also repeatedly stress that athletes should make sure they see the credential and confirm DCOs' identifications," he said.
"What China does is to truly uphold WADA's World Anti-Doping Code," he added.
Sun, the first Chinese man to win an Olympic swimming gold, said in his testimony that he was familiar with CHINADA's high level of doping control process.
"China's doping control has a really high standard. I take training in this area and they (Chinese DCOs) will show me their credentials," said Sun during a hearing which was marred by poor translations.
Before the hearing started, Sun told Xinhua that he intended for all who are following the case to know the truth.
"I want the world to know what happened on the night of September 4, 2018 to prove my innocence. I also want to call on international sports organisations in public to protect the basic rights of athletes," Sun said.
CAS Panel will deliberate and prepare for an Arbitral Award setting out its decision on a later date.
Sun Yang won gold in 200m freestyle at the 2016 Rio Olympic Games, and 400m and 1,500m freestyle at 2012 Olympics in London. The 27-year-old also claimed 200m and 400m freestyle titles at the 2019 FINA World Championships in Gwangju, South Korea.
( With inputs from IANS )