node.jsでテストのカバレッジを取る ref: http://qiita.com/iwata-n@github/items/1e8f629eb5b429a49e6d

file0.js

var gulp = require('gulp');
var istanbul = require('gulp-istanbul');
var mocha = require('gulp-mocha');

gulp.task('pre-test', function () {
  return gulp.src(['routes/*.js'])
    // Covering files
    .pipe(istanbul())
    // Force `require` to return covered files
    .pipe(istanbul.hookRequire());
});

gulp.task('test', ['pre-test'], function () {
  return gulp.src(['test/*.js'])
    .pipe(mocha())
    // Creating the reports after tests ran
    .pipe(istanbul.writeReports())
    // Enforce a coverage of at least 90%
    .pipe(istanbul.enforceThresholds({ thresholds: { global: 90 } }));
});

file1.txt

$ gulp test
[16:53:47] Using gulpfile ~/hoge/gulpfile.js
[16:53:47] Starting 'pre-test'...
[16:53:47] Finished 'pre-test' after 50 ms
[16:53:47] Starting 'test'...


  GET /users
GET /users 200 7.133 ms - 8
    ✓ no param (40ms)


  1 passing (45ms)

-----------|----------|----------|----------|----------|----------------|
File       |  % Stmts | % Branch |  % Funcs |  % Lines |Uncovered Lines |
-----------|----------|----------|----------|----------|----------------|
 routes/   |    76.92 |       50 |       50 |    76.92 |                |
  index.js |       80 |      100 |        0 |       80 |              6 |
  users.js |       75 |       50 |      100 |       75 |            7,8 |
-----------|----------|----------|----------|----------|----------------|
All files  |    76.92 |       50 |       50 |    76.92 |                |
-----------|----------|----------|----------|----------|----------------|


=============================== Coverage summary ===============================
Statements   : 76.92% ( 10/13 )
Branches     : 50% ( 1/2 )
Functions    : 50% ( 1/2 )
Lines        : 76.92% ( 10/13 )
================================================================================
[16:53:47] 'test' errored after 336 ms
[16:53:47] Error in plugin 'gulp-istanbul'