this is the question asked in the BBST course from AST, it really provokes your thinking, to rephrase the question – lets say you are developing a text application, how would you ensure it is displaying the fonts correctly? 
my answer is:
first i will:
compare with typeface standards document in print
compare with similar and existing text editing applications(3 or more) that tops the market
and ensure my application as shown in typeface document, and similar to competitor products
second:
i will check is it showing same in all recommended/intended computers and environments eg: windows, mac etc
third:
only if i am satisfied with above 2 levels:-
i will set different font sizes
i will type all characters in alphabet and all numbers
combination of characters and numbers between
special characters – cover all
i will write different paragraphs and sentences
make a print and compare
copy paste
cut and paste
delete
backspace
select all text
delete all text and retype
and ensure at step three the look is all same.
