Appears in collection : Meeting of the National Research Group on Gravitational Waves

Quasinormal modes in the ringdowns are powerful probes for testing the behaviour of strong-field gravity around the black holes. In this talk, first, I want to quickly review the tests of gravity that are being done using the binary black-hole quasi-normal modes currently. Then I will discuss some possible tests of gravity that can be performed using the next-generation detectors using the quasi-normal modes.