How cancer can be diagonised??what tests are usually performed for that?

Depends: This depends on the type of cancer. Some cancers can be suggested upon blood tests, like with prostate cancer. Some can be found upon testing of the urine like bladder cancer. Some can be found upon testing poop for DNA/genetic changes like with colon cancer. Be aware, that often cancers are diagnosed by multiple studies including imaging and in the end require biopsies to confirm diagnoses.