ICommandWrapper Interface

In NUnit 3, test execution is done using command objects, which are constructed for each test case. Execution of a single test case will generally require multiple nested commands. Some attributes placed on a test method are able to contribute to the chain of commands. For example, MaxTimeAttribute adds a command, which examines the elapsed time to complete a test and fails it if a specified maximum was exceeded.

Attributes add to the command chain by implementing one of the two interfaces that derive from the ICommandWrapper interface. The interfaces are defined as follows:

public interface ICommandWrapper
{
    TestCommand Wrap(TestCommand command);
}

public interface IWrapTestMethod : ICommandWrapper
{
}

public interface IWrapSetUpTearDown : ICommandWrapper
{
}

Attributes should not implement the ICommandWrapper interface directly but should select one of the derived intervaces. NUnit applies the IWrapSetUpTearDown interface before SetUp and after TearDown. It applies the IWrapTestMethod interface after SetUp and before the test is run.

Attributes implementing one of these interfaces must be placed on a test method. Otherwise, they have no effect. The Wrap method should return an appropriate command in which the original command has been nested. For an example, see the implementation of MaxTimeAttribute.

The following NUnit attributes implement the IWrapSetUpTearDown interface:

• MaxTimeAttribute
• RepeatAttribute
• RetryAttribute

The IWrapTestMethodinterface is not currently used by any NUnit attributes.