As i found it is possible to mock result of jooq request . But is it possible to mock fetchInto function for example?
I have this code
val addressSaved = dsl.selectFrom(address)
.where(address.CITY.eq(city))
.fetchOneInto(Address::class.java)
And I want to mock just fetchOneInto. It will make testing more easily I think.
How to mock xyzInto(Class<E>) methods
You can replace the implementation of all the xyzInto(Class<E>) style methods using a single SPI: The RecordMapperProvider as documented here:
https://www.jooq.org/doc/latest/manual/sql-execution/fetching/pojos-with-recordmapper-provider/
That way, irrespective of your specific query, you can always populate custom implementations of your Address class (or even some other subclass). You'll still need to mock the statement itself, though. Probably again using a MockConnection as you already discovered.
Mocking vs integration testing
You've probably made an informed decision regarding mocking vs. integration testing already, but for future visitors of this question, I'm still mentioning this:
In general, it is a lot easier and more useful to just integration test your code with your actual database (e.g. using testcontainers), and if you must mock things to test higher level logic, then mock your services, not jOOQ SQL statements.
Related
Having a class-level variable and instantiating the object at the same time creates a problem for Unit Testing because you can't really mock the dependency.
Does this mean the Kotlin feature by lazy should be avoided as it hinders proper unit testing, or is there a way to overcome this? Thanks.
A lazy is just a val that gets initialised later - if you need to change all your vals to vars so you can poke around at them while testing, that's probably a bad sign.
If your lazy is creating objects, then that's where dependency injection comes in - pass in the dependency, or something that provides the dependency, and then you can mock that when the lazy initialiser calls it.
If you're just trying to change the internal state so you can test a particular scenario, that's trickier. Ideally with a unit test you're testing the behaviour of a single component, and how it interacts with other things - if it provides the expected input and output. You shouldn't need to poke around at the internals, at least not in a way that isn't already part of the design and part of the expected use case.
But sometimes you want to recreate state, which is possible using the normal API, but takes a lot of code. That's a trickier call when the component isn't already designed that way - if it's that important, you might want to make it configurable, either through constructor parameters or by passing in some kind of config object.
Making things public that should be private just for testing is usually a sign that you should find another way to do your test. Changing a val to a var just for testing is especially bad, because it breaks the usual immutability guarantees and now your code has to handle all the "possibly changed" warnings even though you know it's really a val. I don't think lazy really makes much difference here - it's just a fancy getter, an internal implementation detail. I think your issues are more down to how the code is structured, and injecting your dependencies will probably help a lot
I'm not so much seeking a specific implementation but trying to figure out the proper terms for what I'm trying to do so I can properly research the topic.
I have a bunch of interfaces and those interfaces are implemented by controllers, repositories, services and whatnot. Somewhere in the start up process of the application we're using the Castle.MicroKernel.Registration.Component class to register the classes to use for a particular interface. For instance:
Component.For<IPaginationService>().ImplementedBy<PaginationService>().LifeStyle.Transient
Recently I became interested in creating an audit trail of every class and method call. There's a few hundred of these classes so writing a proxy class for each one by hand isn't very practical. I could use a template to generate the code but I'd rather not blow up our code base with all that.
So I'm curious if there's some kind of on the fly solution. I know nHibernate creates proxy classes at some point which overlay all the entity classes. Can someone give me some guidance on how I might be able to do something similar here?
Something like:
Component.For<IPaginationService>().ImplementedBy<ProxyFor<PaginationService>>().LifeStyle.Transient
Obviously that won't work because I can only use generics to generalize the types of methods but not the methods themselves. Is there some tricky reflection approach I can use to do this?
You are looking for what Castle Windsor calls interceptors. It's an aspect-oriented way to tackle cross-cutting concerns -- auditing is certainly one of them. See documentation, or an article about the approach:
Aspect oriented programming is an approach that effectively “injects” pieces of code before or after an existing operation. This works by defining an Inteceptor wrapping the logic being invoked then registering it to run whenever a particular set/sub-set of methods are called.
If you want to apply it to many registered services, read more about interceptor selection mechanisms: IModelInterceptorsSelector helps there.
Using PostSharp, things like this can be even done at compile time. This can speed the resulting application, but when used correctly, interceptors are not slow.
I've had a certain feeling these last couple of days that dependency-injection should really be called "I can't make up my mind"-pattern. I know this might sound silly, but really it's about the reasoning behind why I should use Dependency Injection (DI). Often it is said that I should use DI, to achieve a higher level of loose-coupling, and I get that part. But really... how often do I change my database, once my choice has fallen on MS SQL or MySQL .. Very rarely right?
Does anyone have some very compelling reasons why DI is the way to go?
Two words, unit testing.
One of the most compelling reasons for DI is to allow easier unit testing without having to hit a database and worry about setting up 'test' data.
DI is very useful for decoupling your system. If all you're using it for is to decouple the database implementation from the rest of your application, then either your application is pretty simple or you need to do a lot more analysis on the problem domain and discover what components within your problem domain are the most likely to change and the components within your system that have a large amount of coupling.
DI is most useful when you're aiming for code reuse, versatility and robustness to changes in your problem domain.
How relevant it is to your project depends upon the expected lifespan of your code. Depending on the type of work you're doing zero reuse from one project to the next for the majority of code you're writing might actually be quite acceptable.
An example for use the use of DI is in creating an application that can be deployed for several clients using DI to inject customisations for the client, which could also be described as the GOF Strategy pattern. Many of the GOF patterns can be facilitated with the use of a DI framework.
DI is more relevant to Enterprise application development in which you have a large amount of code, complicated business requirements and an expectation (or hope) that the system will be maintained for many years or decades.
Even if you don't change the structure of your program during development phases you will find out you need to access several subsystems from different parts of your program. With DI each of your classes just needs to ask for services and you're free of having to provide all the wiring manually.
This really helps me on concentrating on the interaction of things in the software design and not on "who needs to carry what around because someone else needs it later".
Additionally it also just saves a LOT of work writing boilerplate code. Do I need a singleton? I just configure a class to be one. Can I test with such a "singleton"? Yes, I still can (since I just CONFIGURED it to exist only once, but the test can instantiate an alternative implementation).
But, by the way before I was using DI I didn't really understand its worth, but trying it was a real eye-opener to me: My designs are a lot more object-oriented as they have been before.
By the way, with the current application I DON'T unit-test (bad, bad me) but I STILL couldn't live with DI anymore. It is so much easier moving things around and keeping classes small and simple.
While I semi-agree with you with the DB example, one of the large things that I found helpful to use DI is to help me test the layer I build on top of the database.
Here's an example...
You have your database.
You have your code that accesses the database and returns objects
You have business domain objects that take the previous item's objects and do some logic with them.
If you merge the data access with your business domain logic, your domain objects can become difficult to test. DI allows you to inject your own data access objects into your domain so that you don't depend on the database for testing or possibly demonstrations (ran a demo where some data was pulled in from xml instead of a database).
Abstracting 3rd party components and frameworks like this would also help you.
Aside from the testing example, there's a few places where DI can be used through a Design by Contract approach. You may find it appropriate to create a processing engine of sorts that calls methods of the objects you're injecting into it. While it may not truly "process it" it runs the methods that have different implementation in each object you provide.
I saw an example of this where the every business domain object had a "Save" function that the was called after it was injected into the processor. The processor modified the component with configuration information and Save handled the object's primary state. In essence, DI supplemented the polymorphic method implementation of the objects that conformed to the Interface.
Dependency Injection gives you the ability to test specific units of code in isolation.
Say I have a class Foo for example that takes an instance of a class Bar in its constructor. One of the methods on Foo might check that a Property value of Bar is one which allows some other processing of Bar to take place.
public class Foo
{
private Bar _bar;
public Foo(Bar bar)
{
_bar = bar;
}
public bool IsPropertyOfBarValid()
{
return _bar.SomeProperty == PropertyEnum.ValidProperty;
}
}
Now let's say that Bar is instantiated and it's Properties are set to data from some datasource in it's constructor. How might I go about testing the IsPropertyOfBarValid() method of Foo (ignoring the fact that this is an incredibly simple example)? Well, Foo is dependent on the instance of Bar passed in to the constructor, which in turn is dependent on the data from the datasource that it's properties are set to. What we would like to do is have some way of isolating Foo from the resources it depends upon so that we can test it in isolation
This is where Dependency Injection comes in. What we want is to have some way of faking an instance of Bar passed to Foo such that we can control the properties set on this fake Bar and achieve what we set out to do, test that the implementation of IsPropertyOfBarValid() does what we expect it to do, i.e. return true when Bar.SomeProperty == PropertyEnum.ValidProperty and false for any other value.
There are two types of fake object, Mocks and Stubs. Stubs provide input for the application under test so that the test can be performed on something else. Mocks on the other hand provide input to the test to decide on pass\fail.
Martin Fowler has a great article on the difference between Mocks and Stubs
I think that DI is worth using when you have many services/components whose implementations must be selected at runtime based on external configuration. (Note that such configuration can take the form of an XML file or a combination of code annotations and separate classes; choose what is more convenient.)
Otherwise, I would simply use a ServiceLocator, which is much "lighter" and easier to understand than a whole DI framework.
For unit testing, I prefer to use a mocking API that can mock objects on demand, instead of requiring them to be "injected" into the tested unit from a test. For Java, one such library is my own, JMockit.
Aside from loose coupling, testing of any type is achieved with much greater ease thanks to DI. You can put replace an existing dependency of a class under test with a mock, a dummy or even another version. If a class is created with its dependencies directly instantiated it can often be difficult or even impossible to "stub" them out if required.
I just understood tonight.
For me, dependancy injection is a method for instantiate objects which require a lot of parameters to work in a specific context.
When should you use dependancy injection?
You can use dependancy injection if you instanciate in a static way an object. For example, if you use a class which can convert objects into XML file or JSON file and if you need only the XML file. You will have to instanciate the object and configure a lot of thing if you don't use dependancy injection.
When should you not use depandancy injection?
If an object is instanciated with request parameters (after a submission form), you should not use depandancy injection because the object is not instanciated in a static way.
I just read the Wikipedia article on mock objects, but I'm still not entirely clear on their purpose. It appears they are objects that are created by a test framework when the actual object would be too complex or unpredictable (you know 100% sure what the values of the mock object are because you fully control them).
However, I was under the impression that all testing is done with objects of known values, so I must be missing something. For example, in a course project, we were tasked with a calendar application. Our test suite consisted of event objects that we knew exactly what they were so we could test the interactions between multiple event objects, various subsystems, and the user interface. I'm guessing these are mock objects, but I don't know why you wouldn't do this because without the objects of known values, you can't test a system.
A mock object is not just an object with known values. It is an object that has the same interface as a complex object that you cannot use in test (like a database connection and result sets), but with an implementation that you can control in your test.
There are mocking frameworks that allow you to create these objects on the fly and in essence allow you to say something like: Make me an object with a method foo that takes an int and returns a bool. When I pass 0, it should return true. Then you can test the code that uses foo(), to make sure it reacts appropriately.
Martin Fowler has a great article on mocking:
http://martinfowler.com/articles/mocksArentStubs.html
Think of the classic case of having client and server software. To test the client, you need the server; to test the server, you need the client. This makes unit testing pretty much impossible - without using mocks. If you mock the server, you can test the client in isolation and vice versa.
The point of the mock is not to duplicate the behaviour of the things its mocking though. It is more to act as a simple state machine whose state changes can be analysed by the test framework. So a client mock might generate test data, send it to the server and then analyse the response. You expect a certain response to a specific request, and so you can test if you get it.
I agree with everything #Lou Franco says and you should definitely read the excellent Martin Fowler article on test doubles that #Lou Franco points you to.
The main purpose of any test double (fake, stub or mock) is to isolate the object under test so that your unit test is only testing that object (not its dependencies and the other types it collaborates or interacts with).
An object that provides the interface that your object is dependent on can be used in place of the actual dependency so that expectations can be placed that certain interactions will occur. This can be useful but there is some controversy around state-based vs. interaction-based testing. Overuse of mock expectation will lead to brittle tests.
A further reason for test doubles is to remove dependencies on databases or file systems or other types that are expensive to set up or perform time consuming operations. This means you can keep the time required to unit test the object you're interested in to a minimum.
Here's an example: if you're writing code that populates a database you may want to check if a particular method has added data to the database.
Setting up a copy of the database for testing has the problem that if you assume there are no records before the call to the tested method and one record after, then you need to roll back the database to a previous state, thus adding to the overhead for running the test.
If you assume there is only one more record than before, it may clash with a second tester (or even a second test in the same code) connecting to the same database, thus causing dependencies and making the tests fragile.
The mock allows you to keep the tests independent of each other and easy to set up.
This is just one example - I'm sure others can supply more.
I agree 100% with the other contributors on this topic, especially with the recommendation for the Martin Fowler article.
You might be interested in our book, see http://www.growing-object-oriented-software.com/. It's in Java, but the ideas still apply.
Many people use Mock Objects when they are writing unit tests. What is a Mock Object? Why would I ever need one? Do I need a Mock Object Framework?
Object Mocking is used to keep dependencies out of your unit test.
Sometimes you'll have a test like "SelectPerson" which will select a person from the database and return a Person object.
To do this, you would normally need a dependency on the database, however with object mocking you can simulate the interaction with the database with a mock framework, so it might return a dataset which looks like one returned from the database and you can then test your code to ensure that it handles translating a dataset to a person object, rather than using it to test that a connection to the database exists.
Several people have already answered the 'what', but here are a couple of quick 'whys' that I can think of:
Performance
Because unit tests should be fast, testing a component that
interacts with a network, a database, or other time-intensive
resource does not need to pay the penalty if it's done using mock
objects. The savings add up quickly.
Collaboration
If you are writing a nicely encapsulated piece of
code that needs to interact with someone else's code (that hasn't
been written yet, or is in being developed in parallel - a common
scenario), you can exercise your code with mock objects once an
interface has been agreed upon. Otherwise your code may not begin to
be tested until the other component is finished.
A mock object lets you test against just what you are writing, and abstract details such as accessing a resource (disk, a network service, etc). The mock then lets you pretend to be that external resource, or class or whatever.
You don't really need a mock object framework, just extend the class of the functionality you don't want to worry about in your test and make sure the class you are testing can use your mock instead of the real thing (pass it in via a constructor or setter or something.
Practice will show when mocks are helpful and when they aren't.
EDIT: Mocking resources is especially important so you don't have to rely on them to exist during the test, and you can mock the details of how they exist and what they respond (such as simulating a FileNotFoundException, or a webservice that is missing, or various possible return values of a webservice)... all without the slow access times involved (mocking will prove MUCH faster than accessing such resources in the test).
Do I need a Mock Object Framework?
Certainly not. Sometimes, writing mocks by hand can be quite tedious. But for simple things, it's not bad at all. Applying the principle of Last Responsible Moment to mocking frameworks, you should only switch from hand-written mocks to a framework when you've proven to yourself that hand-writing mocks is more trouble than it's worth.
If you're just getting starting with mocking, jumping straight into a framework is going to at least double your learning curve (can you double a curve?). Mocking frameworks will make much more sense when you've spent a few projects writing mocks by hand.
Object Mocking is a way to create a "virtual" or mocked object from an interface, abstract class, or class with virtual methods. It allows you to sort of wrap one of these in your own definition for testing purposes. It is useful for making an object that is relied on for a certain code block your are testing.
A popular one that I like to use is called Moq, but there are many others like RhinoMock and numerous ones that I don't know about.
It allows you to test how one part of your project interacts with the rest, without building the entire thing and potentially missing a vital part.
EDIT: Great example from wikipedia: It allows you to test out code beforehand, like a car designer uses a crash test dummy to test the behavior of a car during an accident.
Another use is it will let you test against other parts of your system that aren't built yet. For example, if your class depends on some other class that is part of a feature that someone else is working on, you can just ask for a mostly complete interface, program to the interface and just mock the details as you expect them to work. Then, make sure your assumptions about the interface were correct (either while you are developing, or once the feature is complete).
Whether or not you a mocking framework is useful depends in part on the language of the code you're writing. With a static language, you need to put in extra effort in order to trick the compiler into accepting your mock objects as a replacement for the real thing. In a dynamically-typed language such as Python, Ruby or Javascript, you can generally just attach the methods onto arbitrary object or class and pass that as the parameter -- so a framework would add much less value.
2 recommended mocking frameworks for .net Unit testing are Typemock Isolator and Rhino Mock.
In the following link you can see an explanation from Typemock as to why you need a mocking framework for Unit Testing.