Bottom up Testingtesting the testing flow is from bottom to top.
The process repeated unless the components at the top level of the hierarchy are to be tested. Bottom up is more advantageous became it is easy to create driver rather creating a stub and can serve multiple purposes.
Example: If A, B & C are three Module, if Main module A is under construction. In this testing, the Developer can take the help of a Temporary program that called as Driver to check the communication between the modules.