I worked for a software company where part of my job was to test the upcoming applications and softwares that would be used by the financial tower of my client. There are many tools depending on the type of application involved. For an instance,you would test a java based application with testing the UI by having a login screen and running different kinds of JavaScript queries. There are unit test cases involved in any kind of code. These test cases debug each kind of method, property and instances and produces the result in the final user interface.