According to the docs here you can use
environment["foo"] OR environment.foo
globals["bar"] OR globals.bar
to access them.
ie;
postman.setEnvironmentVariable("foo", "bar");
tests["environment var foo = bar"] = environment.foo === "bar";
postman.setGlobalVariable("foobar", "1");
tests["global var foobar = true"] = globals.foobar == true;
postman.setGlobalVariable("bar", "0");
tests["global var bar = false"] = globals.bar == false;