Why Debye shielding occur in plasma?

Why Debye shielding occur in plasma when we introduce a test charge?

The short answer is that electric fields do work to get rid of themselves.

Does Debye shielding depends on test charge When it is introduced in plasma?

I am not sure what you are asking here but Debye shielding occurs in a plasma because the charges are free to move and electric fields do work to get rid of themselves.