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 one or more TestFixtures from type provided. At least one
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
will be returned nonetheless, labelled as non-runnable.