Tips for Writing Extensions
An Extenders Guide will be published in the future. At the moment, writing an
extension is a bit of an adventure. Extension authors are advised to join the
nunit-developer list and post questions and comments there.
For the moment, the following tips may be of assistance.
- The nunit.core.interfaces assembly is intended to be stable in the future
while the nunit.core assembly will change from release to release. Right now,
both assemblies are still in flux, but extensions that depend solely on the interfaces
assembly will have a much better chance of surviving NUnit version changes. Unfortunately,
this is rather difficult to do without duplicating a great deal of NUnit code. Most
of the add-in samples provided with NUnit are currently version dependent.
- If you place the definition of a custom attribute in the same assembly as your
add-in, then user tests are dependent on the add-in assembly. If the add-in is
version-dependent, then the user tests will also be version-dependent. We suggest
placing any types referenced by user tests in a separate assembly, particularly if
your extension relies on nunit.core.
- If using Visual Studio, set Copy Local to false for any references to nunit.core
or nunit.core.interfaces. This is especially important if you are also building
- There is currently no mechanism to allow decorators to apply in a particular order.
NUnit applies decorators in the order in which they are returned through reflection,
which may vary among different runtimes.
- Avoid trying to "stretch" the existing extension points to do more than they were
intended to do. Rather, let us know what further extension points you would like to see!