We want to introduce property-based testing into our Quarkus project, preferably with jqwik. We already got numerous test cases using junit jupiter. We also use CDI in out test cases.
Getting jqwik running in a small Quarkus example project went well, so I wanted to write some properties in out big project. jqwik is running, however, the #Property, #Example and #Provider methods do not have access to the injected bean (as in: the injected bean is Null, TreeRepository in the example below). Same for ArbitrarySupplier subclasses. If I replace the #Example with a #Test the referring test can access the bean and the test passes.
My first guess is that this has something to do with the jqwik lifecycle. I did not find enough information about how (and if?) jqwik integrates with injection.
How do I get this running?
In the example I expect treeRepository to be an instance of TreeRepository (the class is #ApplicationScoped). Instead it is null, except for in the method with the #Test annotation.
#QuarkusTest
class MyTestClass {
#Inject
TreeRepository treeRepository;
#Test
void testSimple() {
final Collection<Tree> trees = this.treeRepository.getTrees() // works
assertThat(trees).isNotEmpty();
}
#Example
void testSimple() {
final Collection<Tree> trees = this.treeRepository.getTrees() // does not work
assertThat(trees).isNotEmpty();
}
#Property
void treesHaveLeaves(#Forall("tree") Tree tree) { // does not work
assertThat(tree.getLeaves()).isNotEmpty();
}
Arbitrary<Tree> tree() {
final Collection<Tree> trees = this.treeRepository.getTrees(); // does not work
return Arbitraries.of(trees);
}
}
There is bad news and maybe a bit of good news.
The bad news: #QuarkusTest is specially made for use with JUnit Jupiter. Jupiter and jqwik are two different test engines for the JUnit Platform. The lifecycles of different engines do not compose, that's why treeRepository will not be injected automatically when you're executing jqwik properties or examples.
The good news is that it's probably not too difficult to create something like #JqwikQuarkusTest for your integration of jqwik and Quarkus.
If you want to do that yourself you can use jqwik's Spring support as an inspiration or template: https://github.com/jlink/jqwik-spring. Or you read up about jqwik's hooks here: https://jqwik.net/docs/current/user-guide.html#lifecycle-hooks and start from scratch.
If you don't feel up to the task yourself, you might want to think about paying someone to do it for you or your company. I'd be happy to help out.
One of the definition of ninject in internet is;
"Somewhere in the middle of your application, you're creating a class
inside another class. That means you're creating a dependency.
Dependency Injection is about passing in those dependencies, usually
through the constructor, instead of embedding them."
what i want to learn is, where ever we see a creation of a class inside another class should we use ninject or just we should use in some part of program that we want/need to apply loosely coupling for design purposes because maybe we would like to use different approaches in the future?
Sorry if this is a silly question.
It's a perfectly valid question, and there are no absolute right or wrong answers. Ninject and other IoC frameworks are designed to de-couple dependencies.
So the moment you do this:
public class MyClass1
{
public MyClass1()
{
MyClass2 mc2 = new MyClass2();
}
}
You can categorically say that MyClass1 has a dependency in MyClass2.
For me, my rule is this: do I need to unit test MyClass1, or is it likely I'll need to unit test MyClass1?
If I don't need to unit test it, then I don't find much value in decoupling the two classes.
However, if I do need to unit test MyClass1, then injecting in MyClass2 gives you much better control over your unit tests (and allows you to test MyClass1 in isolation).
You do need to evaluate each case separately though. In the above example, if I need to unit test MyClass1, and MyClass2 is just a basic string formatting class, then I probably wouldn't decouple it. However, if MyClass2 was an email sending class then I would de-couple it. I don't want my unit tests actually sending emails, so I would feed in a fake for my tests instead.
So I don't believe there are any solid rules, but hopefully the above gives you a better idea of when you might decouple, and when you might not decouple.
I fully understand the idea of the design of Repository pattern. But why do we need to implement the iDepository interface class? What particular use is this for?
The repository class itself works without the interface class.
I think someone is going to answer me it's for decoupling from the business logic and the data logic.
But even if there is no interface class, isn't the data logic decoupled data logic?
It is so that you can inject a test double of the IRepository class when you are unit testing the business layer. This has the following benefits:
It allows you to easily pinpoint failing tests as being caused by the business layer rather than the repository layer;
It makes your business logic layer tests fast, as they depend neither on data access, which tends to be slow, nor set-up of a database structure and test data, which tends to be very slow.
One way to inject the test doubles when unit testing is by Constructor Injection. Suppose your Repository has the following methods:
void Add(Noun noun);
int NumberOfNouns();
And this is the code of your business class:
public class BusinessClass {
private IRepository _repository;
public BusinessClass(IRepository repository) {
_repository = repository;
}
// optionally, you can make your default constructor create an instance
// of your default repository
public BusinessClass() {
_repository = new Repository();
}
// method which will be tested
public AddNoun(string noun) {
_repository.Add(new Noun(noun));
}
}
To test AddNoun without needing a real Repository, you need to set up a test double. Usually you would do this by using a mocking framework such as Moq, but I'll write a mock class from scratch just to illustrate the concept.
public IRepository MockRepository : IRepository {
private List<Noun> nouns = new List<Noun>();
public void Add(Noun noun) {
nouns.Add(noun);
}
public int NumberOfNouns() {
return nouns.Count();
}
}
Now one of your tests could be this.
[Test]
public void AddingNounShouldIncreaseNounCountByOne() {
// Arrange
var mockRepository = new MockRepository();
var businessClassToTest = new BusinessClass(mockRepository);
// Act
businessClassToTest.Add("cat");
// Assert
Assert.AreEqual(1, mockRepository.NumberOfNouns(), "Number of nouns in repository should have increased after calling AddNoun");
}
What this has achieved is that you have now tested the functionality of your BusinessClass.AddNoun method without needing to touch the database. This means that even if there's a problem with your Repository layer (a problem with a connection string, say) you have assurance that your Business layer is working as expected. This covers point 1 above.
As for point 2 above, whenever you're writing tests which test the database you should make sure it's in a known state before each test. This usually involves deleting all the data at the beginning of every test and re-adding test data. If this isn't done then you can't run assertions against, say, the number of rows in a table, because you won't be sure what that's supposed to be.
Deleting and re-adding test data would normally be done by running SQL scripts, which are slow and vulnerable to breakage whenever the database structure changes. Therefore it's advisable to restrict the use of the database only to the tests of the repository itself, and use mocked out repositories when unit testing other aspects of the application.
As for the use of abstract classes - yes, this would provide the same ability to supply test doubles. I'm not sure which code you would choose to put in the abstract base and which the concrete implementation, though. This answer to an SO question has an interesting discussion on abstract classes vs interaces.
First, you must understand what the Repository pattern is. It's an abstraction layer so that rest of the application do not have to care where the data comes from.
Abstractions in .NET is typically represented by interfaces as no logic (code) can be attached to an interface.
As a bonus that interface also makes it easier for you to test your application since you can mock the interface easily (or create a stub)
The interface also allows you to evolve your data layer. You might for instance start by using a database for all repository classes. But later you want to move some logic behind a web service. Then you only have to replace the DB repository with a WCF repository. You might also discover that an repository is slow and want to implement a simply memory cache within it (by using memcache or something else)
I found a very useful msdn page demonstrating the idea of Repository and Test Driven Development
.
http://blogs.msdn.com/b/adonet/archive/2009/12/17/walkthrough-test-driven-development-with-the-entity-framework-4-0.aspx
I'm trying to understand dependency injections (DI), and once again I failed. It just seems silly. My code is never a mess; I hardly write virtual functions and interfaces (although I do once in a blue moon) and all my configuration is magically serialized into a class using json.net (sometimes using an XML serializer).
I don't quite understand what problem it solves. It looks like a way to say: "hi. When you run into this function, return an object that is of this type and uses these parameters/data."
But... why would I ever use that? Note I have never needed to use object as well, but I understand what that is for.
What are some real situations in either building a website or desktop application where one would use DI? I can come up with cases easily for why someone may want to use interfaces/virtual functions in a game, but it's extremely rare (rare enough that I can't remember a single instance) to use that in non-game code.
First, I want to explain an assumption that I make for this answer. It is not always true, but quite often:
Interfaces are adjectives; classes are nouns.
(Actually, there are interfaces that are nouns as well, but I want to generalize here.)
So, e.g. an interface may be something such as IDisposable, IEnumerable or IPrintable. A class is an actual implementation of one or more of these interfaces: List or Map may both be implementations of IEnumerable.
To get the point: Often your classes depend on each other. E.g. you could have a Database class which accesses your database (hah, surprise! ;-)), but you also want this class to do logging about accessing the database. Suppose you have another class Logger, then Database has a dependency to Logger.
So far, so good.
You can model this dependency inside your Database class with the following line:
var logger = new Logger();
and everything is fine. It is fine up to the day when you realize that you need a bunch of loggers: Sometimes you want to log to the console, sometimes to the file system, sometimes using TCP/IP and a remote logging server, and so on ...
And of course you do NOT want to change all your code (meanwhile you have gazillions of it) and replace all lines
var logger = new Logger();
by:
var logger = new TcpLogger();
First, this is no fun. Second, this is error-prone. Third, this is stupid, repetitive work for a trained monkey. So what do you do?
Obviously it's a quite good idea to introduce an interface ICanLog (or similar) that is implemented by all the various loggers. So step 1 in your code is that you do:
ICanLog logger = new Logger();
Now the type inference doesn't change type any more, you always have one single interface to develop against. The next step is that you do not want to have new Logger() over and over again. So you put the reliability to create new instances to a single, central factory class, and you get code such as:
ICanLog logger = LoggerFactory.Create();
The factory itself decides what kind of logger to create. Your code doesn't care any longer, and if you want to change the type of logger being used, you change it once: Inside the factory.
Now, of course, you can generalize this factory, and make it work for any type:
ICanLog logger = TypeFactory.Create<ICanLog>();
Somewhere this TypeFactory needs configuration data which actual class to instantiate when a specific interface type is requested, so you need a mapping. Of course you can do this mapping inside your code, but then a type change means recompiling. But you could also put this mapping inside an XML file, e.g.. This allows you to change the actually used class even after compile time (!), that means dynamically, without recompiling!
To give you a useful example for this: Think of a software that does not log normally, but when your customer calls and asks for help because he has a problem, all you send to him is an updated XML config file, and now he has logging enabled, and your support can use the log files to help your customer.
And now, when you replace names a little bit, you end up with a simple implementation of a Service Locator, which is one of two patterns for Inversion of Control (since you invert control over who decides what exact class to instantiate).
All in all this reduces dependencies in your code, but now all your code has a dependency to the central, single service locator.
Dependency injection is now the next step in this line: Just get rid of this single dependency to the service locator: Instead of various classes asking the service locator for an implementation for a specific interface, you - once again - revert control over who instantiates what.
With dependency injection, your Database class now has a constructor that requires a parameter of type ICanLog:
public Database(ICanLog logger) { ... }
Now your database always has a logger to use, but it does not know any more where this logger comes from.
And this is where a DI framework comes into play: You configure your mappings once again, and then ask your DI framework to instantiate your application for you. As the Application class requires an ICanPersistData implementation, an instance of Database is injected - but for that it must first create an instance of the kind of logger which is configured for ICanLog. And so on ...
So, to cut a long story short: Dependency injection is one of two ways of how to remove dependencies in your code. It is very useful for configuration changes after compile-time, and it is a great thing for unit testing (as it makes it very easy to inject stubs and / or mocks).
In practice, there are things you can not do without a service locator (e.g., if you do not know in advance how many instances you do need of a specific interface: A DI framework always injects only one instance per parameter, but you can call a service locator inside a loop, of course), hence most often each DI framework also provides a service locator.
But basically, that's it.
P.S.: What I described here is a technique called constructor injection, there is also property injection where not constructor parameters, but properties are being used for defining and resolving dependencies. Think of property injection as an optional dependency, and of constructor injection as mandatory dependencies. But discussion on this is beyond the scope of this question.
I think a lot of times people get confused about the difference between dependency injection and a dependency injection framework (or a container as it is often called).
Dependency injection is a very simple concept. Instead of this code:
public class A {
private B b;
public A() {
this.b = new B(); // A *depends on* B
}
public void DoSomeStuff() {
// Do something with B here
}
}
public static void Main(string[] args) {
A a = new A();
a.DoSomeStuff();
}
you write code like this:
public class A {
private B b;
public A(B b) { // A now takes its dependencies as arguments
this.b = b; // look ma, no "new"!
}
public void DoSomeStuff() {
// Do something with B here
}
}
public static void Main(string[] args) {
B b = new B(); // B is constructed here instead
A a = new A(b);
a.DoSomeStuff();
}
And that's it. Seriously. This gives you a ton of advantages. Two important ones are the ability to control functionality from a central place (the Main() function) instead of spreading it throughout your program, and the ability to more easily test each class in isolation (because you can pass mocks or other faked objects into its constructor instead of a real value).
The drawback, of course, is that you now have one mega-function that knows about all the classes used by your program. That's what DI frameworks can help with. But if you're having trouble understanding why this approach is valuable, I'd recommend starting with manual dependency injection first, so you can better appreciate what the various frameworks out there can do for you.
As the other answers stated, dependency injection is a way to create your dependencies outside of the class that uses it. You inject them from the outside, and take control about their creation away from the inside of your class. This is also why dependency injection is a realization of the Inversion of control (IoC) principle.
IoC is the principle, where DI is the pattern. The reason that you might "need more than one logger" is never actually met, as far as my experience goes, but the actually reason is, that you really need it, whenever you test something. An example:
My Feature:
When I look at an offer, I want to mark that I looked at it automatically, so that I don't forget to do so.
You might test this like this:
[Test]
public void ShouldUpdateTimeStamp
{
// Arrange
var formdata = { . . . }
// System under Test
var weasel = new OfferWeasel();
// Act
var offer = weasel.Create(formdata)
// Assert
offer.LastUpdated.Should().Be(new DateTime(2013,01,13,13,01,0,0));
}
So somewhere in the OfferWeasel, it builds you an offer Object like this:
public class OfferWeasel
{
public Offer Create(Formdata formdata)
{
var offer = new Offer();
offer.LastUpdated = DateTime.Now;
return offer;
}
}
The problem here is, that this test will most likely always fail, since the date that is being set will differ from the date being asserted, even if you just put DateTime.Now in the test code it might be off by a couple of milliseconds and will therefore always fail. A better solution now would be to create an interface for this, that allows you to control what time will be set:
public interface IGotTheTime
{
DateTime Now {get;}
}
public class CannedTime : IGotTheTime
{
public DateTime Now {get; set;}
}
public class ActualTime : IGotTheTime
{
public DateTime Now {get { return DateTime.Now; }}
}
public class OfferWeasel
{
private readonly IGotTheTime _time;
public OfferWeasel(IGotTheTime time)
{
_time = time;
}
public Offer Create(Formdata formdata)
{
var offer = new Offer();
offer.LastUpdated = _time.Now;
return offer;
}
}
The Interface is the abstraction. One is the REAL thing, and the other one allows you to fake some time where it is needed. The test can then be changed like this:
[Test]
public void ShouldUpdateTimeStamp
{
// Arrange
var date = new DateTime(2013, 01, 13, 13, 01, 0, 0);
var formdata = { . . . }
var time = new CannedTime { Now = date };
// System under test
var weasel= new OfferWeasel(time);
// Act
var offer = weasel.Create(formdata)
// Assert
offer.LastUpdated.Should().Be(date);
}
Like this, you applied the "inversion of control" principle, by injecting a dependency (getting the current time). The main reason to do this is for easier isolated unit testing, there are other ways of doing it. For example, an interface and a class here is unnecessary since in C# functions can be passed around as variables, so instead of an interface you could use a Func<DateTime> to achieve the same. Or, if you take a dynamic approach, you just pass any object that has the equivalent method (duck typing), and you don't need an interface at all.
You will hardly ever need more than one logger. Nonetheless, dependency injection is essential for statically typed code such as Java or C#.
And...
It should also be noted that an object can only properly fulfill its purpose at runtime, if all its dependencies are available, so there is not much use in setting up property injection. In my opinion, all dependencies should be satisfied when the constructor is being called, so constructor-injection is the thing to go with.
I think the classic answer is to create a more decoupled application, which has no knowledge of which implementation will be used during runtime.
For example, we're a central payment provider, working with many payment providers around the world. However, when a request is made, I have no idea which payment processor I'm going to call. I could program one class with a ton of switch cases, such as:
class PaymentProcessor{
private String type;
public PaymentProcessor(String type){
this.type = type;
}
public void authorize(){
if (type.equals(Consts.PAYPAL)){
// Do this;
}
else if(type.equals(Consts.OTHER_PROCESSOR)){
// Do that;
}
}
}
Now imagine that now you'll need to maintain all this code in a single class because it's not decoupled properly, you can imagine that for every new processor you'll support, you'll need to create a new if // switch case for every method, this only gets more complicated, however, by using Dependency Injection (or Inversion of Control - as it's sometimes called, meaning that whoever controls the running of the program is known only at runtime, and not complication), you could achieve something very neat and maintainable.
class PaypalProcessor implements PaymentProcessor{
public void authorize(){
// Do PayPal authorization
}
}
class OtherProcessor implements PaymentProcessor{
public void authorize(){
// Do other processor authorization
}
}
class PaymentFactory{
public static PaymentProcessor create(String type){
switch(type){
case Consts.PAYPAL;
return new PaypalProcessor();
case Consts.OTHER_PROCESSOR;
return new OtherProcessor();
}
}
}
interface PaymentProcessor{
void authorize();
}
** The code won't compile, I know :)
The main reason to use DI is that you want to put the responsibility of the knowledge of the implementation where the knowledge is there. The idea of DI is very much inline with encapsulation and design by interface.
If the front end asks from the back end for some data, then is it unimportant for the front end how the back end resolves that question. That is up to the requesthandler.
That is already common in OOP for a long time. Many times creating code pieces like:
I_Dosomething x = new Impl_Dosomething();
The drawback is that the implementation class is still hardcoded, hence has the front end the knowledge which implementation is used. DI takes the design by interface one step further, that the only thing the front end needs to know is the knowledge of the interface.
In between the DYI and DI is the pattern of a service locator, because the front end has to provide a key (present in the registry of the service locator) to lets its request become resolved.
Service locator example:
I_Dosomething x = ServiceLocator.returnDoing(String pKey);
DI example:
I_Dosomething x = DIContainer.returnThat();
One of the requirements of DI is that the container must be able to find out which class is the implementation of which interface. Hence does a DI container require strongly typed design and only one implementation for each interface at the same time. If you need more implementations of an interface at the same time (like a calculator), you need the service locator or factory design pattern.
D(b)I: Dependency Injection and Design by Interface.
This restriction is not a very big practical problem though. The benefit of using D(b)I is that it serves communication between the client and the provider. An interface is a perspective on an object or a set of behaviours. The latter is crucial here.
I prefer the administration of service contracts together with D(b)I in coding. They should go together. The use of D(b)I as a technical solution without organizational administration of service contracts is not very beneficial in my point of view, because DI is then just an extra layer of encapsulation. But when you can use it together with organizational administration you can really make use of the organizing principle D(b)I offers.
It can help you in the long run to structure communication with the client and other technical departments in topics as testing, versioning and the development of alternatives. When you have an implicit interface as in a hardcoded class, then is it much less communicable over time then when you make it explicit using D(b)I. It all boils down to maintenance, which is over time and not at a time. :-)
Quite frankly, I believe people use these Dependency Injection libraries/frameworks because they just know how to do things in runtime, as opposed to load time. All this crazy machinery can be substituted by setting your CLASSPATH environment variable (or other language equivalent, like PYTHONPATH, LD_LIBRARY_PATH) to point to your alternative implementations (all with the same name) of a particular class. So in the accepted answer you'd just leave your code like
var logger = new Logger() //sane, simple code
And the appropriate logger will be instantiated because the JVM (or whatever other runtime or .so loader you have) would fetch it from the class configured via the environment variable mentioned above.
No need to make everything an interface, no need to have the insanity of spawning broken objects to have stuff injected into them, no need to have insane constructors with every piece of internal machinery exposed to the world. Just use the native functionality of whatever language you're using instead of coming up with dialects that won't work in any other project.
P.S.: This is also true for testing/mocking. You can very well just set your environment to load the appropriate mock class, in load time, and skip the mocking framework madness.
I'd like to test a "withCriteria" closure and am not sure how to go about it. I see how to mock out the withCriteria call, but not test the code within the closure. When running the test that executes the "withCriteria", I keep getting a MissingMethodException, even though the code runs fine under the normal flow of execution. Any ideas?
Thanks!
Steve
I wouldn't go that route. Instead I'd move the query into the domain class as a static finder method and test it directly in an integration test with real data. Then you can easily mock the helper method when it's called in a controller or service test.
class YourDomainClass {
...
static List<YourDomainClass> findFooBar() {
YourDomainClass.withCriteria {
...
}
}
}
Then in a unit test:
def results = [instance1, instance2, instance3]
YourDomainClass.metaClass.static.findFooBar = { -> results }
This way you test that the query works against the in-memory database in an integration test but it's easy to mock it in unit tests.
Further to Burt's answer, check out named queries as described here:
http://blog.springsource.com/2010/05/24/more-grails-1-3-features/
You can then mock the property/method access in your unit tests as described by Burt.
Since nobody mentioned the option to create a DSL to run other DSLs here's a full disclosure of this method. I use it quite often with very good results.
Groovy/Grails testing DSLs
There's no mock implementation for Hibernate criteria at the present time. You'll need to use integration tests. However, Burt's recommendation of making this a static finder method is a good one for code organization. You should also look at named queries, described at http://www.grails.org/1.2+Release+Notes, for a nice syntax for this.