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A function stub is a function that can safely be called without error, but it has no definition, so it doesn't actually do anything when we call it.
A 'stub' is a placeholder class or function that doesn't do anything yet, but needs to be there so that the class or function in question is defined.
These terms are often confused so I'll clarify what I mean by them. Stubbing means replacing a method, function or an entire object with a version that produces hard-coded responses. This is typically used to isolate components from each other, and your code from the outside world.
1 : a short part remaining after the rest has been removed or used up a pencil stub. 2 : a small part of a larger piece of printed paper (as a check or ticket) kept as a record of the purpose of the paper.
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<8)
{
try
{
errorService.LogError("long file entered named:" + filename);
}
catch (Exception e)
{
mailService.SendEMail("[email protected]", "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).
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.
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.
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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