IFixtureBuilder
The IFixtureBuilder interface is exposed by a class that knows how to
build a TestFixture from one or more Types. In general, it is exposed
by an attribute, but may be implemented in a helper class used by the
attribute in some cases.
Build a TestFixture from type provided. A non-null TestSuite
must always be returned, since the method is generally called
because the user has marked the target class as a fixture.
If something prevents the fixture from being used, it should
be returned nonetheless, labelled as non-runnable.