What is Function or Component Testing and different types?

Function Testing:
Testing of individual or independent component and verifies the functioning of independent component which is separately testable.
Testing each component like Amount Label is displayed properly or not, Amount Text Box should allow value between 100-1000. Click on Submit button should take the input and navigate to the next page. Cancel should stay in same page. this is called function or component testing.

Positive Testing:
Testing the values with in the range given.
Ex: 101,600,800,1000

Negative Testing:
Testing with the intention of breaking the functionality of the application.
Ex: Hund, 99, 1@1, Blank, -200

Under Testing: 
Not Providing optimal inputs for testing.
Ex: Not entering values within the range 100-1000

Exhaustive Testing or Over Testing:
Testing which is something more than required limit.
Ex: 99,1001

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