Instrument and generate code coverage independent of test runner

npm install gulp-coverage
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Gulp coverage reporting for Node.js that is independent of the test runner


gulp-coverage generates block, line, chainable and statement coverage for Node.js JavaScript files. This is equivalent to function, statement, branch and "modified condition/decision" coverage, where a "statement" is equivalent to a "modified condition/decision". The HTML report gives summary information for the block, line and statement covereage across all the files as well as for each file.


The chainable coverage supports Array-like chainables and will record misses where the chained member calls both receive and result-in an empty list.

HTML report

For each covered file, a chain of links is built allowing you to click through from the summary to the first and then all subsequent instances of each type of miss (line misses and statement misses).

Example Report Showing missed lines, missed statements and chains of links

The HTML report format has been desiged to be accessible and conformant with WCAG 2 Level AA.


To instrument and report on a file using Mocha as your test runner:

    mocha = require('gulp-mocha');
    cover = require('gulp-coverage');

    gulp.task('test', function () {
        gulp.src(['src.js', 'src2.js'], { read: false })
                pattern: ['**/test*'],
                debugDirectory: 'debug'
                outFile: 'coverage.html'

To instrument and report using Jasmine as your test system:

    jasmine = require('gulp-jasmine');
    cover = require('gulp-coverage');

    gulp.task('jasmine', function () {
                pattern: ['**/test*'],
                debugDirectory: 'debug'
                outFile: 'jasmine.html'


There are five different tasks, instrument, gather, report, format and enforce. The instrument task must be run before any of the others can be called and either the gather, or the report task must be run before the enforce or the format task can be run. Enforce can follow format and should be run last if you want the reports generated even when the thresholds have not been met.

After the instrument call, the target files must be required and executed (preferably using some sort of test runner such as gulp-mocha or gulp-jasmine). This will allow the instrumentation to capture the required data (in the example above, this is done by the mocha test runner).

The gulp-coverage gather task will NOT pass any of the original stream files to the subsequent tasks. It must therefore be called after all other stream transformations have occurred.

The Instrument task


pattern - A multimatch glob pattern or list of glob patterns. The globa patterns are relative to the CWD of the process running the gulp file. The pattern 'index.js' will match the index.js file in the same directory as the gulpfile. Globs for file relative to this directory may contain the './'. For example './index.js' is equivalent to 'index.js' (you can also use '**/index.js' to match this file but this will match any other index.js files within the project's directory structure).

The patterns can include match and exclude patterns. In the Mocha and Jasmine examples shown above, there are two JavaScript files test.js and test2.js that are required by the two test files src.js and src2.js. The ** will match these files no matter which directory they live in. Patterns are additive while negations (eg ['/foo*', '!/node_modules//*']) are based on the current set. Exception is if the first pattern is negation, then it will get the full set, so to match user expectation (eg. ['!/foo*'] will match everything except a file with foo in its name). Order matters.

debugDirectory - a string pointing to a directory into which the instrumented source will be written. This is useful for debugging gulp-coverage itself

The Gather Task

The gather task will collate all of the collected data and form this data into a JSON structure that will be placed into the Gulp task stream. It will not pass the original stream files into the stream, so gather cannot be used before another Gulp task that requires the original stream contents.

The format of the JSON structure is a Modified LCOV format. The format has been modified to make it much easier for a template engine like JADE or HAML to generate decorated source code output.

The Modified LCOV JSON format

  lcov : {
         sloc: Integer - how many source lines of code there were in total
         ssoc: Integer - how many statements of code there were in total
         sboc: Integer - how many blocks of code there were in total
         coverage: Float - percentage of lines covered
         statements: Float - percentage of statements covered
         blocks: Float: percentage of blocks covered
         files: Array[Object] - array of information about each file

Each file has the following structure

  file : {
         filename: String - the file
         basename: String - the file short name
         segments: String - the file's directory
         coverage: Float - the percentage of lines covered
         statements: Float - the percentage of statements covered
         blocks: Float - the percentage of blocks covered
         source: Array[Object] - array of objects, one for each line of code
         sloc: Integer - the number of lines of code
         ssoc: Integer - the number of statements of code
         sboc: Integer - the number of blocks of code

Source contains line objects which have the following structure

  line : {
         count: Integer - number of times the line was hit
         statements: Float - the percentage of statements covered
         segments: Array[Object] - the segments of statements that make up the line

Each statement segment has the following structure

  segment : {
       code: String - the string of code for the segment
       count: Integer - the hit count for the segment

The Enforce Task

The enforce task can be used to emit an error (throw an exception) when the overall coverage values fall below your specified thresholds. The default thesholds are 100% for all metrics. This task is useful if you would like the Gulp task to fail in a way that your CI or build system can easily detect.


If you would like to specify thresholds lower than 100%, pass in the thresholds in the first argument to the task. The defaults are:

  options : {
      statements: 100,
      blocks: 100,
      lines: 100

The Format Task

The format task can be used to generate a textual, formatted version of the coverage data and emit this to the Gulp stream. By default, it will call the 'html' formatter (currently only 'html' and 'json' are supported). It will add the formatted text the stream. After calling both gather and format, the stream will contain a vinyl file with an additional attribute called coverage, that contains the JSON formatted data.

The coverage file will be called "coverage.{reporter}" by default and can be output to the disk using gulp.dest(). if the reporter is 'html', then it will be "coverage.html" and if the reporter is 'json', then it will be "coverage.json".

You must call gather prior to calling format.


The task takes one optional argument that contains the options. There are 2 options, here are the default values:

    reporter: 'html',
    outFile: 'coverage.html'

The Report Task (Deprecated)

This task is deprecated because it does not support the gulp.dest task and will probably be removed before the first 1.0.0 release.

Report will generate the reports for the instrumented files and can only be called after instrument has been called. It will also change the stream content for the tasks and pass through the LCOV JSON data so that the enforce task can be run.


outFile - the name of the file into which the report output will be written

reporter - defaults to 'html' - this is the name of the reporter to use. Currently there are an HTML reporter ('html') and a JSON ('json') reporter.

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