Is the test to determine your risks of Brest cancer for only Brest cancer or does the same gene cover your risks of all cancers?

To answer this first you need to consider what cancer is. It is bad, we all know that, but what is cancer actually.

Like most things around you cells have a life cycle. They're created, they do their groovy little things, then they die. You've heard that you're body is replaced every XX years, that is essentially correct. The problem is cancer cells. They don't die right. There is a signal for a cell to die and a cancer cell completely ignores this. On top of that the pathways that control cell division are busted too so they just divide like nobody's business. This is how things go horribly, horribly wrong. They become a burden because they're taking up the body's resources or they're destroying your body's tissue. For example a kidney cancer would destroy your blood's filtration system, toxins build up and you die.

Breast cancer is more benign in so much as the organs that they're inhabiting aren't vital. As Angelina Jolie is showing us, you can live without breasts; it is a very different life but you're alive. I am not trivializing breast cancer. It is a life threatening condition and defiantly something that needs to be taken care of.

How does cancer form is where we need to go next. Everything in a cell is control by your genes. As a cell divides its DNA gets copied. The machinery is efficient but not without it's mistakes. Genes are copied religiously. Every so often there is a mistake. More often than not the copy error is caught and the cell is destroyed. Sometimes it isn't but the error is so significant that it can't survive, or the difference is in an area that the cell doesn't really need.

Then there are the errors in the areas that control cell growth and cell death. These are the ones that might eventually cause cancer, but it is REALLY rare to see them in the same cell at the same time.

If you have a genetic predilection to cancer then the chances get higher. There is a genetic defect in the DNA repair system, the exact gene escapes my recollection, but if it goes bad then your cells are more susceptible to generating cancerous cells. This becomes and issue in tissue that is exposed to carcinogens. For example sunlight is a carcinogen. If you've got this defect you are going to get ocular cancer VERY easily.

Now to the meat of the question. There are genes that are specific to organs that when disabled will increase the likelihood that the cell will turn cancerous. There are a number of these that are specific to some forms of breast cancer. Not all breast cancers, but some. So if they test for these then you can get an idea of your chances but not your absolute chances.

TL;DR: Yes, but it can only test for what it knows and can't test if your susceptible for breast cancers not cause by the genes in question.