JLPT (Japanese Language Proficiency Test)
The Japanese Language Proficiency Test (JLPT, 日本語能力試験) has five levels. Level one (1kyuu, １級) is the hardest and level five (5kyuu, ５級) is the easiest.
In Japan and some other countries, the JLPT is offered twice per year, once in June and then again in December. Unfortunately, in some countries it is only offered in December. It is also fairly expensive- about $50.
I only recommend taking the first and second levels of the test. Levels 3-5 are relatively easy and are probably not worth the travel time and expense of actually taking the exams. They also generally won't help you get a job, so I would instead just spend more time preparing for the 2kyuu and 1kyuu.
What kind of test is the JLPT?
The JLPT requires you to not just get "the gist" of things, but rather understand the subtle points of grammar as well as to demonstrate comprehensive knowledge of kanji.
While the test purports to measure one's ability to communicate generally, it is a multiple choice (four possible answers) format. There is no essay and there is no speaking requirement. However, that doesn't mean it's easy.
Particularly at the hardest level, the JLPT focuses on somewhat obscure grammar which can occasionally trouble even native speakers. For this reason, a significant amount of preparation for the JLPT will be preparing for the test, and not studying the Japanese language in particular.
That said, passing the 1kyuu will help you get a job (or get into grad school) in Japan. The high difficulty level also gives you a bit of a boost when you finally do pass it.