Tutorial: Tagging with --grep

Mocha's --grep feature may be used both on the client (via ?grep=) and server-side. Recent releases of Mocha allow you to also click on the suite or test-case names in the browser to automatically grep them. The concept of tagging utilizes regular grepping, however may be a useful way to keep related tests in the same spot, while still conditionally executing them.

A good example of this is if you wanted to run slow tests only before releasing, or periodically. You could use any sequence of characters you like, perhaps #slow, @slow to tag them as shown here:

describe('app', function () {
  describe('GET /login', function () {
    it('should respond with the login form @fast', function () {
      // ...
    });
  });

  describe('GET /download/:file', function () {
    it('should respond with the file @slow', function () {
      // ...
    });
  });
});

To execute fast tests only then you may do --grep @fast. Another alternative is to only tag @slow, and utilize --grep @slow --invert to invert the grep expression.