6adfeb0 Sep 19, 2013
@alex-seville @medianick
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Advanced Guide (browser version)

This guide details creating a custom reporter, custom adapter, or custom loader for Blanket.js

It is assumed that you have already read the Intermediate guide.


Blanket uses adapters to hook into the test runner, instrument files before the tests, and display the coverage details when the tests complete.

See the Blanket Mocha adapter as an example.

Adapters should be provided as immediately invoked function expressions, i.e.:

    //adapter code

Adapters must implement the following calls:

  1. When the test runner starts it must call blanket.setupCoverage();
  2. When the test module or suite starts it can call blanket.onModuleStart(); (optional)
  3. When a test starts it must call blanket.onTestStart();
  4. When a test ends it must call blanket.onTestDone(<total>, <num passed>)
  5. When all the tests are done it must call blanket.onTestsDone();

Finally, the adapter must call the following function:

    callback: function(){ /* command to start test runner */ }


Custom reporters are used by Blanket to display the coverage results. Blanket comes bundled with a default reporter, but you can create your own.

See the simple_json_reporter as a very basic example of a reporter.

Reporters are functions assigned to blanket.customReporter, which accept the coverage results object as an argument, ex:

(function myReporter(){
    //your reporter code

The example above will create a reporter that will print the coverage result object to the console. Not useful, but it illustrates the pattern.

The coverage result object has the following properties:

  • instrumentation - Will always be set to "blanket"
  • stats - This object has the following properties
    • suites - the number of test suites processed
    • tests - number of tests processed
    • passes - number of tests that passed
    • pending - number of pending tests (should be 0)
    • failures - number of tests that failed
    • start - the datetime that the tests started
  • files - an object containing all the source files covered. Each entry will have the following properties
    • the key is the filename of the source file covered
    • the value consist of two parts
      • an array containing line coverage counts
      • a source property containing an array filled with a string representation of each line of source code

An example coverage result object could be:

    instrumentation: "blanket",
    stats: {
        suites: 1,
        tests: 5,
        passes: 4,
        pending: 0,
        failures: 1,
        start: Dec 15, 16:00:01:034 EST
    files: {
        "sourceFile1.js": {
            1: 3,
            2: null,
            3: 3,
            4: 0,
            5: 3,
            source: [
                "console.log('first line');",
                "//this line is never counted",
                "if (false)",
                "console.log('this line is never executed');",
                "console.log('last line');"


Loaders are used to provide custom requirejs loaders to blanket. CoffeeScript files can be covered in this manner by providing an overriding version of the requirejs coffeescript plugin.

See the coffeescript loader as an example of a loader.