The Datapoint attribute is used to provide data for Theories and is ignored for ordinary tests - including tests with parameters.
When a Theory is loaded, NUnit creates arguments for each of its parameters by using any fields of the same type as the parameter annotated with the DatapointAttribute. Fields must be members of the class containing the Theory and their Type must exactly match the argument for which data is being supplied.
Automatically Supplied Datapoints
It is normally not necessary to specify datapoints for boolean or enum arguments. NUnit automatically supplies values of true and false for boolean arguments and will supply all defined values of any enumeration.
If for some reason you don't wish to use all possible values, you can override this behavior by supplying your own datapoints. If you supply any datapoints for an argument, automatic datapoint generation is suppressed.
For an example of use, see Theory Attribute