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Ask HN: How do you help junior developers learn finding edge cases?

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Ask HN: How do you help junior developers learn finding edge cases?

#1

Post by twy30 »

Edge cases are nature's way of telling us how lousy our programming is. (*1)

Is there a systematic, step-by-step approach to help junior developers improve their awareness/senses of edge cases?

There are some low hanging fruits that are easy to explain and demonstrate. For example, boundary-value analysis [1], division by 0, removal of an item from an empty container, etc. However, sometimes it feels more like art than science (i.e. I know it when I see it. ).

Any feedback and/or idea is greatly appreciated. Thank you.

*1: Borrowed from Dick Guindon's "Writing is nature's way of telling us how lousy our thinking is."

[1]: https://en.wikipedia.org/wiki/Boundary-value_analysis

Re: Ask HN: How do you help junior developers learn finding edge cases?

#2

Post by gostsamo »

List the properties of an object. List the operations performed. Fill in the matrix. Remember it mostly by remembering your own failures.

One should know about all versions of null and empty or overflowed, about stuff being too big, about operations being performed out of sync.

Maybe, the easiest is to ask yourself: What can go wrong? on every line of the code.

Re: Ask HN: How do you help junior developers learn finding edge cases?

#3

Post by twy30 »

gostsamo wrote: post #2

List the properties of an object. List the operations performed. Fill in the matrix. Remember it mostly by remembering your own failures. One should know about all versions of null and empty or overflowed, about stuff being too big, about operations being performed out of sync. Maybe, the easiest is to ask yourself: What can go wrong? on every line of the code.

Thank you. Let me try repeating your advice in my own words:

* Collect all assumptions (regarding data and actions).

* Attack each assumption by throwing known/common/trivial edge cases at it.

* Explore each assumption's necessary conditions: what they are ; how they could possibly be false/broken/absent.

Re: Ask HN: How do you help junior developers learn finding edge cases?

#4

Post by giantg2 »

I find that the majority of edge cases come from the business system (the business has a system/process that we turn into a technical system). I try to approach it like a lawyer trying to find a loophole. Try to ask questions that challenge assumptions about what conditions are possible in the system and ask questions that seem absurd but fit the requirements.

For example, if you're building a financial system maybe ask if a negative balance is allowed. If you charge a fee based on balance (like using basis points), can the fee be negative or is there a set floor? A negative fee sounds stupid, which is why the business probably wouldn't mention it in requirements, but it would be important to set the floor at $0 so if a negative balance occurred, we wouldn't issue a fee.

Re: Ask HN: How do you help junior developers learn finding edge cases?

#5

Post by tudelo »

twy30 wrote: post #3
gostsamo wrote: post #2

List the properties of an object. List the operations performed. Fill in the matrix. Remember it mostly by remembering your own failures. One should know about all versions of null and empty or overflowed, about stuff being too big, about operations being performed out of sync. Maybe, the easiest is to ask yourself: What can go wrong? on every line of the code.

Thank you. Let me try repeating your advice in my own words: * Collect all assumptions (regarding data and actions). * Attack each assumption by throwing known/common/trivial edge cases at it. * Explore each assumption's necessary conditions: what they are ; how they could possibly be false/broken/absent.

These seem like a good set of rules to follow. I would also add that in my experience once you get burned a time or two in production you start to develop a healthy level of paranoia and skepticism towards the code you write. I'm not sure if that step can be skipped, realistically we all create a dumpster fire here and there anyways. A healthy code review process helps as well.

Re: Ask HN: How do you help junior developers learn finding edge cases?

#6

Post by twy30 »

tudelo wrote: post #5
twy30 wrote: post #3

Earlier quoted context omitted.

Thank you. Let me try repeating your advice in my own words: * Collect all assumptions (regarding data and actions). * Attack each assumption by throwing known/common/trivial edge cases at it. * Explore each assumption's necessary conditions: what they are ; how they could possibly be false/broken/absent.

These seem like a good set of rules to follow. I would also add that in my experience once you get burned a time or two in production you start to develop a healthy level of paranoia and skepticism towards the code you write. I'm not sure if that step can be skipped, realistically we all create a dumpster fire here and there anyways. A healthy code review process helps as well.

Thank you. I like your idea. Let me try putting it into a bullet point form:

* Get/give healthy feedback to mitigate against tunnel vision or unknown unknowns.

* Learn from failures and mistakes.

Re: Ask HN: How do you help junior developers learn finding edge cases?

#7

Post by twy30 »

giantg2 wrote: post #4

I find that the majority of edge cases come from the business system (the business has a system/process that we turn into a technical system). I try to approach it like a lawyer trying to find a loophole. Try to ask questions that challenge assumptions about what conditions are possible in the system and ask questions that seem absurd but fit the requirements. For example, if you're building a financial system maybe…

Thank you. That's a great example.

It gave me 2 new directions:

(1) Are there people helping others learn critical thinking? How do they do it?

(2) What does it take to have "user-friendly, tool-assisted critical thinking"? ("formal methods" [1], perhaps?)

I will dig around those 2 directions and see if anything interesting turns up.

[1]: https://en.wikipedia.org/wiki/Formal_methods

Re: Ask HN: How do you help junior developers learn finding edge cases?

#8

Post by giantg2 »

twy30 wrote: post #7
giantg2 wrote: post #4

I find that the majority of edge cases come from the business system (the business has a system/process that we turn into a technical system). I try to approach it like a lawyer trying to find a loophole. Try to ask questions that challenge assumptions about what conditions are possible in the system and ask questions that seem absurd but fit the requirements. For example, if you're building a financial system maybe…

Thank you. That's a great example. It gave me 2 new directions: (1) Are there people helping others learn critical thinking? How do they do it? (2) What does it take to have "user-friendly, tool-assisted critical thinking"? ("formal methods" [1], perhaps?) I will dig around those 2 directions and see if anything interesting turns up. [1]: https://en.wikipedia.org/wiki/Formal_methods

I think I've always just been somewhat contrarian/independent, at least to the level of devil's advocate. My teachers were usually quite annoyed with me when I brought up inconsistencies or loopholes in the assignment.

So, I don't really know how to teach it. Not to mention the negative impacts - it might be a positive for requirement gathering, but my independent views greatly stymie my career advancement. So proceed with caution.

Re: Ask HN: How do you help junior developers learn finding edge cases?

#9

Post by brudgers »

Ask “what edge cases are there?” when first describing the task and let them go off and work a while.

Later ask “are there any other edge cases?” and let them work a while longer.

Repeat as appropriate.

Let them find them on their own for a while or two.

Let them miss them on their own for a while or two.

At the right time ask “have you thought about this potential edge case?”

If you want someone to learn to deal with edge cases, they need to see it is something you value and give them time to learn how to do it.

And how not to do it. “Not” in the logical sense not “not” in a punishment sense or job evaluation sense.

Edge cases are hard and everyone screws them up. The context needs to be safe enough that people can own their mistakes and learn something other than to hide their ignorance.

Good luck.

Re: Ask HN: How do you help junior developers learn finding edge cases?

#10

Post by twy30 »

giantg2 wrote: post #8
twy30 wrote: post #7

Earlier quoted context omitted.

Thank you. That's a great example. It gave me 2 new directions: (1) Are there people helping others learn critical thinking? How do they do it? (2) What does it take to have "user-friendly, tool-assisted critical thinking"? ("formal methods" [1], perhaps?) I will dig around those 2 directions and see if anything interesting turns up. [1]: https://en.wikipedia.org/wiki/Formal_methods

I think I've always just been somewhat contrarian/independent, at least to the level of devil's advocate. My teachers were usually quite annoyed with me when I brought up inconsistencies or loopholes in the assignment. So, I don't really know how to teach it. Not to mention the negative impacts - it might be a positive for requirement gathering, but my independent views greatly stymie my career advancement. So procee…

I understand. It can be a double-edged sword.

I wish you find a place where your talent is valued and appreciated.

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