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What standards are used to evaluate and validate the potential enlightenment one may have achieved in Buddhism?
Do these vary between Theravada and Mahayana traditions, or vary in even more granularity?
Lastly, are these tests/evaluations only generally available to ordained members of the community, or is the knowledge/wisdom of lay members tested as well?
Although the concept of Enlightenment cannot be quantified (much like other emotional changes), from my readings I understand that adept monks or Buddhist practitioners have more control over themselves than average people. For instance, this article discusses how the brain produces more relaxed and wakeful state of mind and brainwaves such as alpha or theta during meditation. I recommend Buddha's Brain that specifically deals with neuroscience of concepts such as happiness, love and wisdom.
Different individuals can have different degrees of enlightenment.
In Zen, validation occurs by recognition by a validated practitioner in a ceremony/event called Dharma Transmission. This is, obviously, broken and basically circular, but every confirmed Zen student can theoretically trace their direct transmission back to Siddhartha Gautama. Inside Zen, there is a known institutional issue of monks conferring Transmission for a pricetag, but there is often a sense of communal vetting of particular teachers (much like this website's reputation system, minus the actual upvotes).
As to what causes a particular teacher to confer Transmission... well, that's up to the teacher and tradition. When students experience kensho or satori, they will often report their experiences to the teacher and the teacher will decide if he or she believes the insight to represent full realization. Some Rinzai schools also confer Transmission to any student who can successfully respond to some pre-defined list of koans.
As to other schools of Buddhism, I am not positive as to the internal workings and methodologies of particular schools, but I do know that, ultimately, validation occurs by already-validated practitioners (much like getting a doctorate).
Wikipedia does a good job of summarizing the four stages of enlightenment, which are stream-enterer, once-returner, non-returner, and arahant. They are distinguished by their remaining attachments such as clinging to rituals, self-view and doubt to an arahant who is fully released.
There are no objective standards for determining the stage of another individual but there are certainly clues. For example, any expression of self-view is undeniable falsification: Insult their mother and see how they react.
However, the stages along the path are subjectively but entirely testable and in minute granularity. All schools of Buddhism recognise the authority of the nikayas/agamas, in which the Buddha describes the dhamma and practice in detail. While many factors are enumerated, in whole the path and attainments are not linear. For example the four material jhanas are sequential but the eight-fold path is better described as cyclical such that the development of each characteristic reinforces the other characteristics of the path. Wisdom, virtue, and concentration are developed in parallel.
Some traditions emphasise an instantaneous enlightenment (chan, zen), some hold a view of a prior enlightened Bodhi nature that must be revealed, while traditionally it was presented as a methodical process. But I don't think it would correct to say that different traditions have different notions of enlightenment. I hesitate here on certain teachers, particularly in Tibetan/bon traditions, who assert the rebirth of arahants. The rebirth of enlightened worthy ones contradicts the Buddha's own definition of nibbana/nirvana, which literally means unbinding, fading out, the end of rebirth, not entering any womb. But rebirth is difficult to objectively test without some fancy super-mundane instruments.
Namo tassa bhagavato arahato samma-sambuddhassa
In the name of Blessed One, the Exalted One (arahant), the fully-(self)-Enlightened One
Among the enlightened, there is a semantic distinction between buddhas, arahants, with residue and without. A buddha is self-realised while an arahant followed the path of a buddha. An enlightened one with residue is still supported by the khandas (he has a body and is alive) while after death (paranibbana) an enlightened one is not supported by the khandas, not supported by a body, is dead and will not return to any womb.
Perhaps a more useful question, if I may: "How does one choose a worthy teacher?"
First, Zen is not considered Buddhism by most because they do not follow any Buddhist Doctrines. I have practiced Nichiren Shoshu True Buddhism http://www.USABuddhism.com since 1974. Enlightenment is Happiness. Happiness is subjective. Go through the Temple websites and study Ichinen Sanzen.
It is self-validating; you don't need to check with anyone to know whether it is correct.
By extension, only a realized meditator can validate the realization of another.
