How can I perform a reference equals in Groovy?

Use is for testing object identity:

groovy:000> class Foo { }
===> true
groovy:000> f = new Foo()
===> Foo@64e464e4
groovy:000> g = new Foo()
===> Foo@47524752
groovy:000> f.is(g)
===> false
groovy:000> g.is(f)
===> false
groovy:000> f.is(f)
===> true

You use the is method. ie:

a.is( b )

See the docs for more description

edit

Since groovy 3, you can use === (or !== for the opposite)