What does to stub mean in programming

Question

For example  what does it mean in this quote      Integrating with an external API is almost a guarantee in any modern web app  To effectively test such integration  you need to stub it out  A good stub should be easy to create and consistently up-to-date with actual  current API responses  In this post  we   ll outline a testing strategy using stubs for an external API

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This phrase is almost certainly an analogy with a phase in house construction — "stubbing out" plumbing. During construction, while the walls are still open, the rough plumbing is put in. This is necessary for the construction to continue. Then, when everything around it is ready enough, one comes back and adds faucets and toilets and the actual end-product stuff. (See for example How to Install a Plumbing Stub-Out.)

When you "stub out" a function in programming, you build enough of it to work around (for testing or for writing other code). Then, you come back later and replace it with the full implementation.

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In this context  the word  stub  is used in place of  mock   but for the sake of clarity and precision  the author should have used  mock   because  mock  is a sort of stub  but for testing  To avoid further confusion  we need to define what a stub is   In the general context  a stub is a piece of program  typically a function or an object  that encapsulates the complexity of invoking another program  usually located on another machine  VM  or process - but not always  it can also be a local object   Because the actual program to invoke is usually not located on the same memory space  invoking it requires many operations such as addressing  performing the actual remote invocation  marshalling serializing the data arguments to be passed  and same with the potential result   maybe even dealing with authentication security  and so on  Note that in some contexts  stubs are also called proxies  such as dynamic proxies in Java    A mock is a very specific and restrictive kind of stub  because a mock is a replacement of another function or object for testing  In practice we often use mocks as local programs  functions or objects  to replace a remote program in the test environment  In any case  the mock may simulate the actual behaviour of the replaced program in a restricted context    Most famous kinds of stubs are obviously for distributed programming  when needing to invoke remote procedures  RPC  or remote objects  RMI  CORBA   Most distributed programming frameworks libraries automate the generation of stubs so that you don t have to write them manually  Stubs can be generated from an interface definition  written with IDL for instance  but you can also use any language to define interfaces     Typically  in RPC  RMI  CORBA  and so on  one distinguishes client-side stubs  which mostly take care of marshaling serializing the arguments and performing the remote invocation  and server-side stubs  which mostly take care of  unmarshaling deserializing the arguments and actually execute the remote function method  Obviously  client stubs are located on the client side  while sever stubs  often called skeletons  are located on the server side   Writing good efficient and generic stubs becomes quite challenging when dealing with object references  Most distributed object frameworks such as RMI and CORBA deal with distributed objects references  but that s something most programmers avoid in REST environments for instance  Typically  in REST environments  JavaScript programmers make simple stub functions to encapsulate the AJAX invocations  object serialization being supported by JSON parse and JSON stringify   The Swagger Codegen project provides an extensive support for automatically generating REST stubs in various languages

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You have also a very good testing frameworks to create such a stub  One of my preferrable is Mockito There is also EasyMock and others    But Mockito is great you should read it - very elegant and powerfull package

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A stub is a controllable replacement for an Existing Dependency  or collaborator  in the system  By using a stub  you can test your code without dealing with the dependency directly   External Dependency - Existing Dependency  It is an object in your system that your code under test interacts with and over which you have no control   Common examples are filesystems  threads  memory  time  and so on   Forexample in below code   public void Analyze string filename                if filename Length lt 8                        try                               errorService LogError  long file entered named     filename                             catch  Exception e                                mailService SendEMail  admin hotmail com    ErrorOnWebService    someerror                                    You want to test mailService SendEMail   method  but to do that you need to simulate an Exception in your test method  so you just need to create a Fake Stub errorService object to simulate the result you want  then your test code will be able to test mailService SendEMail   method  As you see you need to simulate a result which is from an another Dependency which is ErrorService class object  Existing Dependency object

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RPC Stubs   Basically  a client-side stub is a procedure that looks to the client as if it were a callable server procedure  A server-side stub looks to the server as if it s a calling client  The client program thinks it is calling the server  in fact  it s calling the client stub  The server program thinks it s called by the client  in fact  it s called by the server stub  The stubs send messages to each other to make the RPC happen    Source

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Stubbing-out a function means you ll write only enough to show that the function was called  leaving the details for later when you have more time    From  SAMS Teach yourself C    Jesse Liberty and Bradley Jones

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Stub is a function definition that has correct function name  the correct number of parameters and produces dummy result of the correct type    It helps to write the test and serves as a kind of scaffolding to make it possible to run the examples even before the function design is complete

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Stub is a piece of code which converts the parameters during RPC  Remote procedure call  The parameters of RPC have to be converted because both client and server use different address space  Stub performs this conversion so that server perceive the RPC as a local function call

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Layman s terms  it s dummy data  or fake data  test data   etc   that you can use to test or develop your code against until you  or the other party  is ready to present receive real data  It s a programmer s  Lorem Ipsum    Employee database not ready  Make up a simple one with Jane Doe  John Doe   etc  API not ready  Make up a fake one by creating a static  json file containing fake data

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A stub  in this context  means a mock implementation   That is  a simple  fake implementation that conforms to the interface and is to be used for testing

[api] What does "to stub" mean in programming?

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