What is the difference between functional and non-functional testing ?

Functional testing is a kind of testing whose cases of tests are based on the specific conditions of the component of the software that is under test. Inputs are fed to the function and the resulting output is examined. In this type of testing, the internal structure of the software source code or the program is not known. Functional testing can be considered as a kind of black box testing. Functional testing checks a program against specifications of the program and design of the documents. This kind of testing involves basically 5 steps.
The first being the identification of the functions expected to be performed by the software.
The second step involves the creation of data for input according to the specifications of the functions.
In the third step the output after processing of data is determined according to the specifications of the functions.
The fourth step deals with the execution of the cases of the tests.
The actual output is compared with the expected output in the last and final fifth step of the functional testing.

Functional testing forms a crucial part in software processes. What all does functional testing do ?
Functional testing is used to check performance.
Functional testing tests the graphical user interface (GUI) of the program.
Functional testing requires checking the whole program from one end to the other end.
This helps to ensure performance and quality.
It helps in developing programs faster.
Errors also result during functional testing which should be corrected with supporting unit tests.
Later they should be checked once more and verified with a functional test.
Functionality tests have got a great benefit. Many correct tests means the program is correct and working.
Functional testing increases the probability of automatically checking the program.
Functional testing is used to validate the whole input output conversion process.

To make functional testing more effective a process called “continuous integration relentless testing” should be implied. Functional testing is done according to business requirements as stated by client’s specifications. The various aspects of functional testing are listed below:
1. Smoke testing
2. Sanity testing
3. Unit testing
4. Top down testing
5. Bottom up testing
6. Interface testing
7. Usability testing
8. Regression testing
9. Alpha and beta testing
10. System testing
11. Pre user acceptance testing
12. White box testing
13. Black box testing
14. User acceptance testing
15. Globalization testing
16. Localization testing
In contrast to functional testing, the non- functional testing of a software application tests it for non-functional features and requirements. Sometimes there is an overlap of scope of various non functional tests amidst many non- functional requirements. Therefore, in such cases the names of the non functional tests are interchanged to avoid confusion. There are various aspects of non functional testing which have been listed below:
1. Documentation testing
2. Compliance testing
3. Baseline testing
4. Compatibility testing
5. Recovery testing
6. Localization testing
7. Performance testing
8. Endurance testing
9. Load testing
10. Internalization testing
11. Volume testing
12. Stress testing
13. Usability testing
14. Resilience testing
15. Scalability testing and
16. Security testing
In addition to the above mentioned aspects, the non- functionality testing also covers the following additional features:
1. Load testing
2. ergonomics testing
3. migration testing
4. penetration testing
5. data conversion testing
6. operational testing
7. network security testing
8. system security testing
9. installation testing
There’s a basic difference in both types of testing which is that the functional testing tells one what software does whereas non functional testing shows one how well the software executes.