1. Testing

2. Testing Problems  Not Just for Testers!  Although testers are obviously asked more testing problems, developers will often be asked testing problems as well.  Why?  Because a good developer knows how to test their code!

3. Types of Testing Problems  Explain how you would test this real world object (pen, paperclip, etc).  Explain how you would test this computer software (e.g., a web browser).  Write test cases / test code to test this specific method.  We’ll discuss type #1, since it’s usually the most daunting.

4. How to Test A Real World Object  Let’s imagine that you were asked to test a paperclip.  The first thing to understand is: what is it expected to be used for and who are the expected users.  Ask your interviewer—the answer may not be what you think!  The answer could be “by teachers, to hold papers together” or it could be “by artists, to bend into new shapes.”  These two use-cases will have very different answers.

5. How to Test A Real World Object  Once you understand the intended use, think about:  What are the specific use cases for the intended purpose?  holding 2 sheets of paper together, and up to 30 sheets.  If it fails, does it fail gracefully?  What does it mean for it to fail?  Answer: “Failing gracefully“ means for the paperclip to not hold paper together.  If it snaps easily, that’s (probably) not failing gracefully.  What are the expectations of it being used outside of the intended use case?  Should we ensure that it has a minimum of usefulness for the other cases?  What “stress” conditions might your paperclip be used in?  Answer: hot weather, cold weather, frequent re-use, etc.

6. How would you test a pen?  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.

7. Solution  Interviewer: How would you test a pen?  Candidate: Let me find out a bit about the pen. Who is going to use the pen?  Interviewer: Probably children.  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.  Candidate: Ok, great. On what? Paper? Clothing? Walls?  Interviewer: On clothing.  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.I s that correct?

8. solution  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:  Does the pen wash off with warm water, cold water, and luke warm water?  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?  Is the pen safe (e.g.—non-toxic) for children?  and so on...

9. Problem  How would you test an ATM in a distributed banking system?