How does the development of agile testing vary from other methodologies of testing development?

In what way does agile testing (development) methodology differ from the other testing (development) methodologies?

The methodology followed by Agile testing requires the code to be broken down into small units and only one unit is worked upon or tested at a time. This is not the case with other testing methodologies. This agile process practiced by the team focuses on one particular unit of the code through continuous communication. This method is more flexible.