Do Singapore work visa holders need to contribute to CPF (social security fund)?

No.
Neither employment pass holders nor their employers (on behalf of EP
holders) are required to make CPF or any other statutory fund
contributions. CPF contributions are required only for Singapore
citizens and permanent residents. CPF was established in 1955 and is
basically a savings scheme to provide protection for locals (Singapore
citizens and permanent residents) in their old age.

Is a medical test required when applying for work pass in Singapore?