As a first step look here:-
http://www.ukba.homeoffice.gov.uk/si...glish-language
On the right-hand side of the page there is a link for the new approved listing from UKBA for providers of English language courses and tests:-
http://www.ukba.homeoffice.gov.uk/si...lish-tests.pdf
The UKBA site states that,
"In the test, you will need to demonstrate a basic command of English (speaking and listening) at level A1 of the Common European Framework of Reference Someone assessed at level A1 can understand and use simple, everyday expressions and very basic phrases.
You will not need to demonstrate your reading and writing skills. The minimum standard that you must meet is in speaking and listening at level A1 of the Common European Framework of Reference."
Most of the various English tests are quite expensive. In the region of about P7000 - P8500
Looking at right-hand side of the UKBA approved list, under the heading of 'Contact details' you will find the links for the approved providers.
May I suggest that you review the links and find a testing centre that offers an appropriate test at reasonable cost, close to where your wife live. Many of these test centres also arrange review classes for those whose self-confidence needs a boost.
Plenty of people here have been through the process and will help you with any specific questions.