There are two standardised tests widely used as part of the admissions procedure for postgraduate courses in the USA and Canada, in some other countries. These are the GRE and the GMAT.
The Graduate Record Examination (GRE) is a standardised aptitude test which includes a General Test and Subject Tests. The General Test, which is required by most US universities, measures verbal reasoning, quantitative reasoning, and analytical writing skills; the Subject Tests, which are less frequently required, measure achievement in specific subject areas. The General Test is a computer-based test which is available on a year-round basis in Dublin. Full details of this test, together with sample questions and registration procedures, can be accessed on the GRE website at www.gre.org. You can download a document with further details on the GRE here
The Graduate Management Admissions Test (GMAT) is used for applying to MBA courses or other postgraduate management courses in universities all over the world. This is also a computer-adaptive test that measures basic verbal, mathematical and analytical writing skills. As with the GRE, it is possible to take this test on a year-round basis in Dublin. Full details of this test, together with sample questions and registration procedures, can be accessed on the GMAT website at: www.mba.com.
Most US universities require you to submit the test results as part of your application package so you would need to register for a test well in advance of the application deadline.