Official German Language Proficiency Examinations
There are different types of German language examinations that people take for various purposes. Some individuals just have to pass an exam at school while others need to prove to their employer that they possess adequate German language skills. Hence, different German language examinations (as well as certificates) exist in different parts of the world but not all of them are universally accepted. Anybody who would someday like to study or work in Germany or another German-speaking country will need to take an official German language proficiency examination. There are quite a few of them and they all serve different purposes.
There basically are three major institutions that provide German language proficiency testing and issue official language certificates which are widely accepted in the German-speaking countries (Germany, Austria, Switzerland and Luxemburg) and these include: the Goethe Institute and telc gGmbH (both from Germany) and Verein ÖSD (from Austria). There certainly are also other private institutions that offer language examinations but their certificates may not be as widely accepted even though they follow the Common European Framework of Reference (CEFR) for languages. So, your best bet is to take those provided by the three institutions mentioned above. Choose one according to your needs and/or the test centre location (their test centres are located in most countries of the world). If you need a certificate for a specific purpose (e.g., university studies), find out first which of them is accepted by your counterparty.
Types of German Language Proficiency Examinations
There are several types of German language proficiency examinations divided according to their purpose whereas for each purpose a different level and scope of language skills may be required. Some exams of a certain type can be provided by all three above mentioned agencies while others only by one of them. For example, foreign spouses from the third countries need a German language certificate to be allowed to move to Germany for family reunification, foreigners residing in Germany have to pass a German language test before they can apply for German citizenship, foreign students who want to study at German schools and universities also need to prove they possess adequate language skills while foreigners planning to move to Germany to take up an employment may also be required by their employers to pass a language examination to qualify for the job.
As it was mentioned earlier there are different levels of language skills that may be required within each category (e.g., a middle school and a university may have different requirements or there may be different language proficiency criteria for a doctor and a nursing assistant) so it is best to clarify this well in advance. When it comes to physical locations where you can take these examinations you should check with the provider as they have many tests centres located around the world which are operated either by themselves or by their partners. To help you make yourself ready for a German language proficiency examination here is a link to a collection of downloadable samples of German language proficiency tests from all three major certifying agencies we mentioned above.