This is primarily necessary to test Fitnesse itself. We need the ability to show that Fitnesse will correctly fail a test when comparing different expected and actual values, but we need that test to turn GREEN so we don't have failing tests!

Works for primatives

int fixture
field	field?
21	fail[37]

Works for strings

string fixture
field	field?
some value	fail[some other value]

Works for objects (people)

person fixture
field	field?
Joe Smith	fail[Joe Smithe]

You can even use the fail keyword to prove that the fail keyword works. In this test, we wrap "fail[Joe Smith]" inside a fail - so when the application returns a person named "Joe Smith", which fails to fail (get it?), the test PASSES!

person fixture
field	field?
Joe Smith	fail[fail[Joe Smith]]

And this one shows that "Joe Smith" (correctly) does not equal "failure[Joe Smith]"

person fixture
field	field?
Joe Smith	fail[failure[Joe Smith]]