What method did GATTACA use to test their workers?

The method used by GATTACA to test their workers involved analyzing blood samples. In the film, genetic testing plays a crucial role in determining a person's social status and career opportunities. Blood is rich in DNA, providing a comprehensive view of an individual's genetic makeup, which is why it was chosen as the method for testing.

Blood testing allows for the identification of various genetic markers, which can indicate a person's predisposition to certain traits or diseases. This practice illustrates the film's central theme of genetic determinism, where individuals are judged based on their genetic profiles rather than their abilities or character. By focusing on blood samples, GATTACA demonstrates the invasive and critical nature of genetic evaluation in the society depicted in the film, where one's genetic identity defines their reality and limits their potential.

Other methods such as urine, hair, or saliva samples could potentially offer DNA analysis, but blood samples provide the most accurate and comprehensive results in the context of the film's narrative and the societal implications of genetic testing.