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Re: [TDD] Unit tests and parameter validation

John Goodsen #35377 Think in terms of the contract between the caller and the code. ?The code guarantees valid results, ONLY IF the caller guarantees they'll pass in valid parameters. ?So if passing a null is not part of that contract, you should not have to write tests and code to check if a null was passed. ?Can you imagine if you started down the path of littering all your code with "if (foo == null) throw new Exception("Foo cannot be null") at the beginning of each method? ?Don't do that. there's a big difference between checking is something is null and checking that a value is "valid". ?Checking if a parameter is null is a code smell in most cases. ?The only reason I'd ever check if something was null was if that lurking null pointer exception might not be found until later on in the program execution - in that case, I might Fail Early by throwing an exception. In the case of validating that the value pass passes some business validation rules, that might be an object waiting to be born, where you could check in a constructor that somebody is creating a bad object (e.g. the class "invariant") .. and I'd fail right there and then - you shouldn't have code later on that checks validity of values - don't let them be created in the first place. toggle quoted message Show quoted text On Tue, Oct 15, 2013 at 10:41 AM, Eb <amaeze@...> wrote: Donald - If a test passes in the wrong input and fails initially, I see 3 general ways of getting the test to pass: Have your test look for the exception that will be thrown by the code Have your code validate the parameters to prevent an exception from being thrown? Have you code substitute (handle in some other way) the bad parameter so that an exception is not thrown Or is the assumption that my code should never call the method with a bad parameter, hence I shouldn't have a test that tests with bad parameter? Thanks. On Tue, Oct 15, 2013 at 1:25 PM, Donaldson, John <john.m.donaldson@...> wrote: ? Eb, ? I agree with Colin in principle, but wider than that I’d say, following Uncle Bob’s rule of “no code without a failing test” pretty well ensures you will have tests which supply incorrect inputs, if you want to handle those cases. ? John D. ? From: testdrivendevelopment@... [mailto:testdrivendevelopment@...] On Behalf Of Colin Vipurs Sent: 15 October 2013 18:52 To: testdrivendevelopment@... Subject: Re: [TDD] Unit tests and parameter validation ? If this is internal code only and the code calling it is also testing then I not only would I not test it but I'd remove all defensive code guards as well. ?For example, a typical pattern would be: ? public void foo(SomeObject bar) { ? ?if (bar == null) { ? ?..... ? ?} } ? Instead of catching the null and handling it, ensure all code calling it will never pass in null. ?Cuts down on both test and production code. ? On Tue, Oct 15, 2013 at 5:03 PM, Eb <amaeze@...> wrote: ? Hello everyone - ? I'm curious to know thoughts on writing tests that specify the behavior of a method when its inputs are incorrect. ?Is this a common practice. ?How about parameter validation in this case? ?Having some healthy debate on it and wanted to get other insight. ? The context for this in a class/methods that are used within an internal application - this is not an API that will be publicly exposed to external consumers. ? Thanks. ? -- blog: twitter: @eikonne ? -- Maybe she awoke to see the roommate's boyfriend swinging from the chandelier wearing a boar's head. Something which you, I, and everyone else would call "Tuesday", of course. -- blog: twitter: @eikonne -- jgoodsen@... Public PGP

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#35377

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