mocha not running all tests in test dir

This is my folder structure

src/
   a.js
   b.js
   test/
     a.spec.js
     b.spec.js

and I've tried running

1. ~/.../src $ mocha
2. ~/.../src $ mocha test
3. ~/.../src $ mocha test/
4. ~/.../src $ mocha ./test/
5. ~/.../src $ mocha ./test/*.js

but non worked... all I get is just one test file running and the rest are ignored.

The docs say that (1) should do the job but well it doesn't.