The most commonly accepted test by accredited MBA programs is the GMAT, or Graduate Management Admission Test. This test was created specifically for testing management aptitude and is the business school equivalent of law school's LSAT.
The GMAT is divided into three sections: analytical, quantitative and verbal. The analytical portion is composed of two essays for which you must read and write an analysis, one dealing with an argument and the other pertaining to a particular issue.
The GMAT's quantitative section is composed of 37 multiple choice questions split between problem solving and data sufficiency. The verbal section of the GMAT consists of 41 multiple choice questions based around sentence correction, critical reasoning and reading comprehension.
The GRE, or Graduate Record Examination, is a graduate school test used primarily for entrance into master's programs in the arts and sciences, but is also accepted by some business schools. The GRE is not as commonly accepted as the GMAT, as the test is not designed specifically to test business or management aptitude.
Despite it not being purpose designed like the GMAT, the GRE contains the same three sections with similar questions and testing theory.
If you are not a native English speaker, then you need to take the TOEFL, or Test of English as a Foreign Language. This is the most common test for establishing fluency in the English language; however, some schools also accept the IELTS, or the International English Language Test System.
Every MBA program has its own admission standards and utilizes your test results in different ways when considering you as a candidate for admission. Some schools establish a baseline score that is a combination of your undergraduate GPA and your GMAT or GRE score. If you do not meet the baseline you will not make it any further in the applicant pool.
Some programs, however, use a formula to calculate your undergraduate GPA and admission test scores and choose the best of the applicant pool for admission without using a baseline score to weed out candidates.
Your business and work experience, recommendations and leadership positions will also enter into this calculus and be considering with varying weight depending upon the MBA program you are applying.