Regarding wasting time on 50% tests... it depends what your system is. In most of the systems (the no mission critical ones, no general libraries) I like to use the 80%/20% rule. I always ask: what are the 20% of the tests that deliver 80% of the value?
You learn with experience but if you do not have it, this is a simple way to learn (as a team).
During the sprint, have people write down:
1 - The tests that actually failed and found a real problem before the code was shipped.
2 - The tests you wrote for the bugs that were found in production during the sprint. If you haven't written the test yet, ask: what kind of test would have found this bug?
Have people in the team share in the retrospective meeting. If you need more time at the beginning you can hold a meeting just for bug sharing. Discuss about the patterns. Commit to write more of these kind of tests.
In a few sprint, you should see regression bugs going down. If you also take a look at the tests than never fail, you will also have a sense of the bugs you should not write.
Let me know how it goes!
Just checking: Did you mean "the tests you should not write"?
I don't personally believe this is the case, but I also can't tell you I know it to be false. What I do know is that types have a non-zero cost, and I think sometimes that's ignored, and only their benefits are acknowledged. But the efforts to bring types to historically dynamic languages show that not all common dynamic language idioms are amenable to reasonable type signatures. While some idioms (e.g. monkey patching) are problematic, that's not the case of all of them.
That aside, that "bit" of typing can amount to a lot. Python programs are usually very compact compared to statically typed languages. Yes, this means writing more unit tests to cover the bits the type checker would have caught, but in my experience the total LOC with unit tests for 100% coverage in Python is still less than a statically types language.
That said, I still prefer statically types languages. The big difference between statically typing and unit tests is when the error is caught. Static typing catches the errors very early. In fact in modern IDE's that do incremental compiles it's literally after you have typed the statement. Errors that hang around tend to ripple through your code because your mental model is wrong, so catching them early means less errors in total. The effect can be large.
The way I see it there are two kinds of costs type systems may impose. Very simplistic type systems, such as the ones in C, Go, and even C++, Java, C#, often force you to write code that is too specific, thus forcing duplication (C and Go especially suffer terribly from not having generics - in Go especially its impossible to write a well typed function that can be passed an array of any kind and return an element of that array).
On the other hand, of your type system is powerful enough, you still get a similar problem when trying to write code that is abstract enough to be reusable, but specific enough to be safe.
For example, if you were writing code for a physical simulation system, you would want to have all quantities carry their measurement unit in their type, to avoid mismatches.
However, you wouldn't want to rewrite maths code for each measurement unit. However, to properly keep track of types in complex maths code gets pretty ugly pretty quickly. For example, a function that wants to compute the scalar product of 2 2-dimensional vectors would only work if the first values of each vector have the same/convertible units as the second pair, in any order (m,s dot s,m should be ok). If you move to matrix multiplication, the types become even more complicated, and this is still very basic algebra. If you want your function to be applicable to arbitrary matrix sizes you're already writing a complex library.
First, static typed languages often simply subtract features that would be available in dynamic languages. So, that's a cost that's paid on day zero, and it can be easy to forget about.
Secondly, there are absolutely times when something that is conceptually easy to describe is a real beast to model in a type system. Think DSLs for SQL, for example. A non-trivial amount of time can be lost fighting these battles.
Dynamic languages are not helpful just because they let you write bugs faster.
Shit at 50% off is still shit. You're not being paid to produce shit, even if you might be really, really efficient at doing so.
Now try serializing things in XML instead of JSON. But not one type of message, multiple types, with flexible formats.
"Oh but this never happens" except it does.
Not to mention the iteration speed whenever you need to fix something.
Apart from both json and XML are a PITA to work with in the first place
How would I do that with a type system?
I also agree, as years ago I wrote a large amount of javascript which had type assertions pretty much everywhere. They didn't take long to write but I'm very glad I did them, and I'd rather have the language do it to save me time, clutter and maintenance.
Lax typing is a real cost. I've been working on some SQL I inherited and even SQL's not-too-bad typing allowed the original coder to mix types where I wouldn't, and create potential runtime errors eg. to assign the contents of a 64-bit integer field to an 32-bit integer field. That's legal and gives no warning. It's also suddenly a runtime error when it exceeds 2^31 (and there are other possible consequences such as screwing up the optimiser). I'd much rather it forced me to match types exactly, or explicitly cast.
In a typed, compiled language you get some pretty nice guarantees just by getting your code compiled. In a dynamic language, you have no way to know if your code even runs until you have 100% code coverage.
Maybe my understanding is wrong, but what you described doesn't seem like a unit test. I think the appropriate term for a test like this at the junction of UI, business logic and code-level triggers is 'feature test', 'integration test', or maybe even just 'test'.
You could use Coq, Isabelle, or Lean. Their type systems are powerful enough to allow such checks.
You can then assert and type against the warning function, the printing function you could only assert against with output buffering or something like that but in my mind that's less likely to go wrong anyway
Keep your type system simple, custom types beyond in built primitives cause head aches imo
Given that transferFunds shows a warning over that 95% threshold, what type of change is going to break that logic? Some sort of botched code rewrite where values doesn't retain their meanings? That batchMode shouldn't trigger the warning? That race condition between the check and the actual transfer?
Most of the unit testing I see is more like test-of-defintions (is fullName still 80 characters wide and doesn't accept null bytes?) which confuses me because a definition can only be correct or incorrect in context.
I accept the usefulness in dynamic languages in the absence of types. My Personal preference is for tests to be a bit higher level (does login with a username containing null still cause an exception?) but I have come to terms with the fact that few people agree with me across multiple organizations, so there must be some point to this trivial testing that is completely lost on me.
These tests are great, but what if username has a bunch of validations on it?
For example, it's reasonable to think a username field might be validated with:
- Must be required
- Within 1-32 characters that match a certain pattern (let's say a regex to limit it to lowercase letters, numbers and -)
- Must not be a blacklisted word (admin, administrator, etc.)
- Must be unique (enforced with a database index)
Pretty standard stuff. Are you going to write 5 integration tests for this? 4 to test each validation and then the success case? These would be tests that exercise your entire web framework's routing stack from request to response (ie. the user visiting a /register URL and then submitting the form).
Personally I would not. I would write 1 unit test for each of those things (4 unhappy cases where I assert a specific validation error for each invalid input and 1 happy case where with valid input I expect 0 validation errors). In this case, the "unit" would likely be a `register_user` function that accepts params as input and either aborts with validation errors, or succeeds by writing the record to the DB.
Then, for an integration test I would have 2 tests. One to make sure with invalid input I end up with some type of error displayed in the HTML response (it doesn't matter which one), and another test with the success case to make sure things work when they should (such as the user is registered and a new record was created in the DB).
So I end up with a tiny bit of overlap in tests. Technically the unit test for the success case doesn't need to be there since the integration test covers it but I usually include it for the sake of completeness because it's usually like 4 lines of code to make that test but I'm not 100% opposed to someone saying it should be left out.
Yes, exactly. It's supposed to catch the rewrite where somebody turns (a * 100) / b > 95 into (a / b) * 100 > 95 and suddenly, the code doesn't work anymore.
Showing a warning is full scenario - it has a whole UX. If this warning is important enough to have a PM, a UX designer, and be translated into 20 languages, it's important enough for the engineer to make sure it actually shows up when its supposed to.
What you describe is a real use case that I personally want to have tested on a real system with all the stuff in place (but test database instead of the real one). It has nothing to do with one unit you can test on its own.
And the crucial problem here is that you tie your testing code on the inner workings of transferFunds, when you are mocking stuff.
> and verify that the warning is triggered when the value being transferred is over 95% of the amount in the account.
Please also note that you cannot verify this property using testing. You can only verify that this works for one particular set of values (or a big but finite set of values). Testing never can verify that something always works. That's the wrong tool for this job.
I, as a user of your software, only care about the feature, and that the feature works. I don't care about testability, whatever that means. And since I case about features, I think this entails that features have to be tested end to end, and not some unrelated classes ("mocks") that are not even used in the final product.
> is easy and makes the resulting code better (eg, easy to replace the notification manager).
It might or it might not. I have seen too much code which was written way too complex which a lot of unnecessary classes and interfaces, just for the sake of "testability". However, some features did not work every once in a while.
If you have the need for different notification backends, go ahead. Even if you need a notification manager (whatever this is) for this. But don't make code more complicated (sometimes called "test-induced design damage") without need.
Or are you talking here about completely different type system ?