gulpfile.js

var gulp = require('gulp');
var $ = require('gulp-load-plugins')();

gulp.task('default', ['watchJs', 'watchTests']);

// make sure you do not start a path with ./
// there's some bug in gaze that causes globs with ./ to not fire
var unitTestPaths = [
  'tests/**/*_tests.js'
];

var jsPaths = [
  'build/app/js/**/*.js'
];



function mochaPipe() {
  return $.mocha({ reporter: 'spec' });
}

gulp.task('watchJs', function() {
  $.watch({ 
      glob: jsPaths, 
      read: false 
    }, 
    function() {
      gulp.start('allUnitTests');
    }
  );

});

// 
gulp.task('watchTests', function() {
  $.watch({
      glob: unitTestPaths
    }, 
    function(files) {
      return files
        .pipe(mochaPipe())
      ;
  }); 
});

gulp.task('allUnitTests', function() {
  return gulp.src(unitTestPaths, {read: false})
    .pipe(mochaPipe())
    ;
});

package.json

{
  "name": "gulp-mocha-watch",
  "version": "0.2.0",
  "dependencies": {},
  "devDependencies": {
    "chai": "^1.9.1",
    "gulp": "^3.8.7",
    "gulp-load-plugins": "^0.5.3",
    "gulp-mocha": "^1.0.0",
    "gulp-watch": "^0.6.9"
  },
  "engines": {
    "node": ">=0.10.26"
  }
}