# Bootstrapper

Most of FakeItEasy's functionality is directly triggered by client code: creating a fake, configuring a call and making assertions about calls are all explicitly invoked and are controllable by various input parameters.

Some behavior is triggered implicitly. FakeItEasy initializes itself when its classes are first accessed. The Bootstrapper allows users to customize the initialization process.

## What does the Bootstrapper do?

At present, the Bootstrapper provides only one service:

• GetAssemblyFileNamesToScanForExtensions provides a list of absolute paths to assemblies that should be scanned for extension points.
The default behavior is to return an empty list.

## How can the behavior be changed?

Provide an alternative bootstrapper class and ensure that it is loaded in the current AppDomain before FakeItEasy is initialized (often this means just including it in your test assembly).

The best way to provide an alternative implementation is to extend FakeItEasy.DefaultBootstrapper. This class defines the default FakeItEasy setup behavior, so using it as a base allows clients to change only those aspects of the initialization that need to be customized.

### An example: returning a specific extra assembly scan for extensions

Most often, FakeItEasy extension points will be defined in assemblies that are already loaded at the time that FakeItEasy is used. In some cases, extensions may reside in assemblies that are not (yet) loaded. Perhaps the extensions are distributed in a shared assembly that does not need to be referenced by any other code. The following bootstrapper can be used to force an additional assembly to be scanned for extension points.

public class ScanAnExternalAssemblyBootstrapper : FakeItEasy.DefaultBootstrapper
{
public override IEnumerable<string> GetAssemblyFilenamesToScanForExtensions()
{
return new [] { @"c:\full\path\to\another\assembly.dll" };
}
}


## How does FakeItEasy find alternative bootstrappers?

Just before the first Bootstrapper function needs to be accessed, FakeItEasy checks all the assemblies currently loaded in the AppDomain. Each assembly is examined for exported types that implement FakeItEasy.IBootstrapper. The first such type that is not FakeItEasy.DefaultBootstrapper is instantiated and used. If no such type is found, then FakeItEasy.DefaultBootstrapper is used.

Note that there is no warning provided if FakeItEasy finds more than one custom bootstrapper implementation. One will be chosen non-deterministically.