Renamed the class to EmptyCustomization.
Added code block regions

and renamed some classes to TestClass.
Deleted the FixtureType property.
Deleted the constructor

with the fixturing parameter.
Deleted the overidable CreateCustomization method.
Deleted unnecessary test types.
Modified the XML documentation.
Introduced the constructor

with customization types and the Customization property.
Added the guard for a null argument.
Renamed the class to BaseFixtureFactory.
Added the omitted implementation and test.
Renamed the class and the local variable.
Implemented customizing a fixture

with instances of customization types passed from the constructor.
Refactored the SpecAttribute class.
Deleted the unnecessary word 'fixturing'

in the custom dictionary for code analysis.
Incremented patch version

in order to indicate that this resolves confusion about which is used to
construct and customize a fixture between constructor parameters and
overridable methods. To do it, this deleted the constructor with the
fixturingType parameter and instead, introduced the new constructor
having the customizationType parameter. Moreover to avoid the confusion,
the overridable CreateCustomization method was deleted. This causes
breaking changes but as it is serious design fault, this is released as
patch version on this major version(v2).