How to test a pen

Problem

How would you test a pen?

Solution
This problem is largely about understand the constraints: what exactly is the pen?

You should ask a lot of questions to understand what exactly you are trying to test To illustrate the technique in this problem, let us guide you through a mock-conversation.
Interviewer: How would you test a pen?

1. Candidate : What kind of pen is it? Is it a ball pen, pilot pen, roller pen, sketch pen?
   Interviewer : sketch pen
2. Candidate: Let me find out a bit about the pen Who is going to use the pen?
   Interviewer: Probably children
3. Candidate: Ok, that’s interesting. What will they be doing with it? Will they be writing, drawing, or doing something else with it?
   Interviewer: Drawing
4. Candidate: Ok, great. On what? Paper? Clothing? Walls?
   Interviewer: On clothing
5. Candidate: Great. What kind of tip does the pen have? Felt? Ball point? Is it intended to wash off, or is it intended to be permanent?
   Interviewer: It’s intended to wash off

… many questions later
Candidate: Ok, so as I understand it, we have a pen that is being targeted at 5—10 year olds. The pen has a felt tip and comes in red, green, blue and black. It’s intended to wash off clothing. Is that correct?


The candidate now has a problem that is significantly different from what it initially seemed to be. Thus, the candidate might now want to test:

1. Does the pen wash off with warm water, cold water, and luke warm water?
2. Does the pen wash off after staying on the clothing for several weeks? What happens if you wash the clothing while the pen is still wet?
3. Is the pen safe (e.g. non-toxic) for children?
4. Drop pen for certain height?

and so on…

Also, test cases have to divided into usability, compatibility, robustness and so on.
In usability we can discuss points like color of ink etc, in compatibility we can discuss the different surfaces where ink can be used,  robustness may have points what happens when it falls from certain heights.

10 cases for testing pen

1. Pen’s ink should be dark so that normal human eyes can read clearly
2. Pen should be continuously in writing mode
3. Pen’s ink color and the pen’s body, cap color should be same so that easy to understand the requirement for user
4. Pen should have the soft grip at the middle place for usability
5. Pen should be in continuously writing mode under hottest and coolest temperature
6. If pen drops from the several feet then also it should be in continuously writing mode if ink is available in pen
7. Pen should not have “Use and throw” type
8. Pen’s refill should be replaceable
9. Paper should be straight and clean
10. Paper should not too smooth and too hard

References
http://tianrunhe.wordpress.com/2012/04/05/how-to-test-a-pen/