Final answer:
The defense mechanism in the described scenario, where a person dismisses test results in favor of attributing symptoms to a bladder infection, is known as denial.
Step-by-step explanation:
The defense mechanism being displayed in the statement "The test must be wrong. I just have a bladder infection." is denial. Denial is a defense mechanism where an individual refuses to accept reality or facts, essentially pretending that a painful event, thought, or feeling does not exist. It is often used to protect the ego from things that the individual cannot cope with. In this case, by insisting that the test results are wrong and attributing health concerns to a mere bladder infection, the person is not accepting a potentially more serious diagnosis or reality.