I am writing unit tests for some async sections of my code (returning Futures) that also involves the need to mock a Scala object.
Following these docs, I can successfully mock the object's functions. My question stems from the fact that withObjectMocked[FooObject.type] returns Unit, where async tests in scalatest require either an Assertion or Future[Assertion] to be returned. To get around this, I'm creating vars in my tests that I reassign within the function sent to withObjectMocked[FooObject.type], which ends up looking something like this:
class SomeTest extends AsyncWordSpec with Matchers with AsyncMockitoSugar with ResetMocksAfterEachAsyncTest {
"wish i didn't need a temp var" in {
var ret: Future[Assertion] = Future.failed(new Exception("this should be something")) // <-- note the need to create the temp var
withObjectMocked[SomeObject.type] {
when(SomeObject.someFunction(any)) thenReturn Left(Error("not found"))
val mockDependency = mock[SomeDependency]
val testClass = ClassBeingTested(mockDependency)
ret = testClass.giveMeAFuture("test_id") map { r =>
r should equal(Error("not found"))
} // <-- set the real Future[Assertion] value here
}
ret // <-- finally, explicitly return the Future
}
}
My question then is, is there a better/cleaner/more idiomatic way to write async tests that mock objects without the need to jump through this bit of a hoop? For some reason, I figured using AsyncMockitoSugar instead of MockitoSugar would have solved that for me, but withObjectMocked still returns Unit. Is this maybe a bug and/or a candidate for a feature request (the async version of withObjectMocked returning the value of the function block rather than Unit)? Or am I missing how to accomplish this sort of task?
You should refrain from using mockObject in a multi-thread environment as it doesn't play well with it.
This is because the object code is stored as a singleton instance, so it's effectively global.
When you use mockObject you're efectibly forcefully overriding this var (the code takes care of restoring the original, hence the syntax of usign it as a "resource" if you want).
Because this var is global/shared, if you have multi-threaded tests you'll endup with random behaviour, this is the main reason why no async API is provided.
In any case, this is a last resort tool, every time you find yourself using it you should stop and ask yourself if there isn't anything wrong with your code first, there are quite a few patterns to help you out here (like injecting the dependency), so you should rarely have to do this.
Related
I am writing unit tests for a complex application which has so many rules to be checked into a single flow by using NUnit and Playwright in .Net5. Actually the case is, to save the time for writing the test scripts for Playwright (front-end testing tool), we have used a library named Bogus to create dummy data dynamically based on the rules (because the test cases has numerous rules to be checked and it was much more difficult to write fresh data to every case). I am using Playwright script into the NUnit test and providing the data source by using [TestCaseSource("MethodName")] to provide dynamic data object for different cases.
Now, we are facing a problem that some of the tests cases get passed and some are failed and we are unable to identify that particularly which test case is causing the problem because the testcase data is being provided by the dynamic source and in that source the data is being generated by the Bogus library on the bases of the rules which we have generated. Plus, we cannot look at the tests for a long time that's why we have automated the process.
[Test]
[TestCaseSource("GetDataToSubmit")]
public async Task Test_SubmitAssignmentDynamicFlow(Assignment assignment)
{
using var playwright = await Playwright.CreateAsync();
await using var browser = await playwright.Chromium.LaunchAsync(new BrowserTypeLaunchOptions
{
Headless = false,
...
});
....
private static IEnumerable<TestCaseData> GetDataToSubmit()
{
//creating data for simple job
var simpleAssignment = new DummyAssigmentGenerator()
....
.Generate();
yield return new TestCaseData(simpleAssignment);
....
Now, my question is, is there any way so that we can view that what were the actual values in the object in the failed case, when we see the whole report of the testcases? So that we can come to know that which certain values are causing problems and eventually fixed those.
Two approaches...
Assuming that DummyAssignmentGenerator is your own class, override its ToString() method to display whatever you would like to see. That string will become part of the name of the test case generated, like...
Test_SubmitAssignmentDynamicFlow(YOUR_STRING)
Apply a name to each TestCaseData item you yield using the SetName() fluent method. In that case, you are supplying the full display name of the test case, not just the part in parentheses. Use {m}(YOUR_STRING) in order to have it appear the same as in the first approach.
If you can use it, the first approach is clearly the simpler of the two.
I have several functions that deal with database interactions. (like readModelById, updateModel, findModels, etc) that I try to use in a functional style.
In OOP, I'd create a class that takes DB-connection-parameters in the constructor, creates the database-connection and save the DB-handle in the instance. The functions then would just use the DB-handle from "this".
What's the best way in FP to deal with this? I don't want to hand around the DB handle throughout the entire application. I thought about partial application on the functions to "bake in" the handle, but that creates ugly boilerplate code, doing it one by one and handing it back.
What's the best practice/design pattern for things like this in FP?
There is a parallel to this in OOP that might suggest the right approach is to take the database resource as parameter. Consider the DB implementation in OOP using SOLID principles. Due to Interface Segregation Principle, you would end up with an interface per DB method and at least one implementation class per interface.
// C#
public interface IGetRegistrations
{
public Task<Registration[]> GetRegistrations(DateTime day);
}
public class GetRegistrationsImpl : IGetRegistrations
{
public Task<Registration[]> GetRegistrations(DateTime day)
{
...
}
private readonly DbResource _db;
public GetRegistrationsImpl(DbResource db)
{
_db = db;
}
}
Then to execute your use case, you pass in only the dependencies you need instead of the whole set of DB operations. (Assume that ISaveRegistration exists and is defined like above).
// C#
public async Task Register(
IGetRegistrations a,
ISaveRegistration b,
RegisterRequest requested
)
{
var registrations = await a.GetRegistrations(requested.Date);
// examine existing registrations and determine request is valid
// throw an exception if not?
...
return await b.SaveRegistration( ... );
}
Somewhere above where this code is called, you have to new up the implementations of these interfaces and provide them with DbResource.
var a = new GetRegistrationsImpl(db);
var b = new SaveRegistrationImpl(db);
...
return await Register(a, b, request);
Note: You could use a DI framework here to attempt to avoid some boilerplate. But I find it to be borrowing from Peter to pay Paul. You pay as much in having to learn a DI framework and how to make it behave as you do for wiring the dependencies yourself. And it is another tech new team members have to learn.
In FP, you can do the same thing by simply defining a function which takes the DB resource as a parameter. You can pass functions around directly instead of having to wrap them in classes implementing interfaces.
// F#
let getRegistrations (db: DbResource) (day: DateTime) =
...
let saveRegistration (db: DbResource) ... =
...
The use case function:
// F#
let register fGet fSave request =
async {
let! registrations = fGet request.Date
// call your business logic here
...
do! fSave ...
}
Then to call it you might do something like this:
register (getRegistrations db) (saveRegistration db) request
The partial application of db here is analogous to constructor injection. Your "losses" from passing it to multiple functions is minimal compared to the savings of not having to define interface + implementation for each DB operation.
Despite being in a functional-first language, the above is in principle the same as the OO/SOLID way... just less lines of code. To go a step further into the functional realm, you have to work on eliminating side effects in your business logic. Side effects can include: current time, random numbers, throwing exceptions, database operations, HTTP API calls, etc.
Since F# does not require you to declare side effects, I designate a border area of code where side effects should stop being used. For me, the use case level (register function above) is the last place for side effects. Any business logic lower than that, I work on pushing side effects up to the use case. It is a learning process to do that, so do not be discouraged if it seems impossible at first. Just do what you have to for now and learn as you go.
I have a post that attempts to set the right expectations on the benefits of FP and how to get them.
I'm going to add a second answer here taking an entirely different approach. I wrote about it here. This is the same approach used by MVU to isolate decisions from side effects, so it is applicable to UI (using Elmish) and backend.
This is worthwhile if you need to interleave important business logic with side effects. But not if you just need to execute a series of side effects. In that case just use a block of imperative statements, in a task (F# 6 or TaskBuilder) or async block if you need IO.
The pattern
Here are the basic parts.
Types
Model - The state of the workflow. Used to "remember" where we are in the workflow so it can be resumed after side effects.
Effect - Declarative representation of the side effects you want to perform and their required data.
Msg - Represents events that have happened. Primarily, they are the results of side effects. They will resume the workflow.
Functions
update - Makes all the decisions. It takes in its previous state (Model) and a Msg and returns an updated state and new Effects. This is a pure function which should have no side effects.
perform - Turns a declared Effect into a real side effect. For example, saving to a database. Returns a Msg with the result of the side effect.
init - Constructs an initial Model and starting Msg. Using this, a caller gets the data it needs to start the workflow without having to understand the internal details of update.
I jotted down an example for a rate-limited emailer. It includes the implementation I use on the backend to package and run this pattern, called Ump.
The logic can be tested without any instrumentation (no mocks/stubs/fakes/etc). Declare the side effects you expect, run the update function, then check that the output matches with simple equality. From the linked gist:
// example test
let expected = [SendEmail email1; ScheduleSend next]
let _, actual = Ump.test ump initArg [DueItems ([email1; email2], now)]
Assert.IsTrue(expected = actual)
The integrations can be tested by exercising perform.
This pattern takes some getting-used-to. It reminds me a bit of an Erlang actor or a state machine. But it is helpful when you really need your business logic to be correct and well-tested. It also happens to be a proper functional pattern.
I understand what recursive functions are, but consider the following example of a function meant to get the local version of data on an item, check if there is new data about it available online based on locally stored cache time, and if there is, updating the local data with the new version, returning up-to-date data about it either way.
function getItemData(id){
var local=getLocalItemData(id);
if(!local.cacheTime.upToDate()){
var newData=getOnlineItemData(id);
updateLocalItemData(id, newData);
return getItemData(id);
}
else{
return local.returnHumanReadable();
}
}
My argument against considering it a recursive function is the fact that it will only end up calling itself on rare occasions when the cache time indicates the data has expired, and that the function only calls itself for convenience.
Instead of using return getLocalItemData(id).returnHumanReadable(); I can use return getItemData(id); because it will return the same result, as the newly saved data won't need to be refreshed again in the several microseconds it will take the function to call itself. Also, it is much shorter: in the actual code, I would use lower level commands instead of those function calls, resulting in code duplication which would make the entire function harder to read and maintain.
So, do you think that my argument makes any sense, or do you consider this to be nothing more than a matter of code organization?
The short answer is: yes it is recursive
It becomes important if you consider a platform that does not support recursion
Since it can call itself, your code will not work on that platform because it is technically recursion
For a trivial case like this replacing the recursive call with getLocalItemData(id).returnHumanReadable(); will allow it to work on this platform. In fact, you can change your code to:
function getItemData(id){
var local=getLocalItemData(id);
if(!local.cacheTime.upToDate()){
var newData=getOnlineItemData(id);
updateLocalItemData(id, newData);
local=getLocalItemData(id);
}
return local.returnHumanReadable();
}
NOTE: If you cannot 100% guarantee that only one call is needed, change the if to while
I am writing a DSL for expressing flow (original I know) in groovy. I would like to provide the user the ability to write functions that are stored and evaluated at certain points in the flow. Something like:
states {
"checkedState" {
onEnter {state->
//do some groovy things with state object
}
}
}
Now, I am pretty sure I could surround the closure in quotes and store that. But I would like to keep syntax highlighting and content assist if possible when editing these DSLs. I realize that the closure COULD reference artifacts from the surrounding flow definition which would no longer be valid when executing the closure in a different context, and I am fine with this. In reality I would like to use the closure syntax for a non-closure function definition.
tl;dr; I need to get the closure's code while evaluating the DSL so that it can be stored in the database and executed by a script host later.
I don't think there is a way to get a closure's source code, as this information is discarded during compilation. Perhaps you could try writing an AST transformation that would make closure's syntax tree available at runtime.
If all you care about is storing the closure in the database, and you don't need later access to the source code, you can try serializing it and storing the serialized form.
Closure implements Serializable, and after nulling its owner, thisObject and delegate attributes I was able to serialize it, but I'm getting ClassNotFoundException on deserialization.
def myClosure = {a, b -> a + b}
Closure.metaClass.setAttribute(myClosure, "owner", null)
Closure.metaClass.setAttribute(myClosure, "thisObject", null)
myClosure.delegate = null
def byteOS = new ByteArrayOutputStream()
new ObjectOutputStream(byteOS).writeObject(myClosure)
def serializedClosure = byteOS.toByteArray()
def input = new ObjectInputStream(new ByteArrayInputStream(serializedClosure))
def deserializedClosure = input.readObject() // throws CNFE
After some searching, I found Groovy Remote Control, a library created specifically to enable serializing closures and executing them later, possibly on a remote machine. Give it a try, maybe that's what you need.
I find that in my daily Flex/Flash work, I do this number a lot:
//Calling a function...
MyCustomObject(container.getChildAt(i)).mySpecialFunction();
The question is - is this the best way to do this? Should I do this:
//Calling a function
var tempItem:MyCustomObject = container.getChildAt(i) as MyCustomObject;
tempItem.mySpecialFunction();
It might be incidental but I'm just wondering if there is an "accepted" way or a preferred way to do this. The second option seems more readable but I wonder if it takes more of a performance hit to create a new variable. Or does it all come down to style and preference?
It's important to remember that there is a difference between explicit casting and using the as keyword. Casting throws an error when it fails, whereas the as keyword does not (it just returns null).
// a casting error
try {
var number:int = 666;
var urlreq:URLRequest = URLRequest( number );
} catch(e:TypeError) {
// TypeError: Error #1034: Type Coercion failed: cannot
// convert 666 to flash.net.URLRequest.
trace(e);
}
Whereas the as keyword fails silently:
var number:int = 666;
var urlreq:URLRequest = number as URLRequest;
trace(urlreq); // prints null to the debug pane
Personally, I bear these behaviours in mind when deciding method to use. Generally, I'd recommend casting explicitly, as you'll know exactly how/when a cast failed. Often, though, you might want to fail silently and continue.
It generally doesn't matter. Creating a var just creates a pointer to the object, so it's not using more memory or anything like that.
The second example is definitely more readable and debuggable and should thus be preferred.
The risk you run from creating temp vars is that you might delay or prevent garbage collection for that object. This generally isn't a problem when it's just a local var in a function; just keep scope in mind when you're creating vars and passing them around.
For in-depth on the subject, read Grant Skinner's series on resource management in AVM2:
http://www.gskinner.com/blog/archives/2006/06/as3_resource_ma.html
for the second example you might want to test for the nullity to avoid a NullPointerException when invoking "mySpecialFunction", e.g.
var tempItem:MyCustomObject = container.getChildAt(i) as MyCustomObject;
if ( tempItem )
{
tempItem.mySpecialFunction();
}
I usually prefer the second approach but you have to remember that you can only use the as operator for casting "Date" and "Array" types.