Testing a module or component independently to verify its expected output is called component testing. Generally component testing is done to verify the functionality and/or usability of a component but not restricted to only these. A component can be of anything which can take inputs and delivers some output.
A connection that integrates two components are called interface. Testing these interfaces are called Interface testing. Interface testing is also same as of a component but differs in its type. Interfaces are widely web services,APIs, connection strings that doesn’t have an UI but takes an input and delivers an output