How do I access mocha's json report from a script? - node.js

Question

Mocha can be invoked from a script and it has a useful JSON reporter, but how can one access that reported structure from the invoking script? Redirecting stdout worked:
var Mocha = require('mocha');
var stats = {};
var oldWrite = process.stdout.write;
process.stdout.write = function(txt) {
stats = JSON.parse(txt).stats; // write invoked in one gulp.
};
new Mocha().
addFile("test/toyTest").
reporter("json", {stats: stats}).
run(function (failures) {
process.on('exit', function () {
process.stdout.write = oldWrite;
console.log("percentage: " + stats.passes/(stats.passes+stats.failures));
process.exit(failures > 0 ? 1 : 0);
});
});
but I'd have expected a more direct solution.

Answer 1

According to the code, the answer was "you can't":
process.stdout.write(JSON.stringify(obj, null, 2));
Since the my solution above is somewhat less than obvious, I created a pull request to add a reporter option to pass in a target object:
var Mocha = require('mocha');
var report = {};
new Mocha().
addFile("test/toyTest").
reporter("json", {"output-object": report}).
run(function (failures) {
process.on('exit', function () {
var s = report.stats;
console.log("percentage: " + s.passes/(s.passes+s.failures));
process.exit(failures > 0 ? 1 : 0);
});
});
which saves capturing process.stdout.write as well as the needless serialization and deserialization of the report structure. I also added a command line to set the output file so you can run:
mocha -R json --reporter-options output-file=rpt.json

Answer 2

An alternative solution is to create your own reporter like it has been suggested in the documentation. I simply copied the json reporter in node_modules/mocha/lib/reporters/json.js to new file in my project folder companyReporter.js and replaced this line
Ln 69: process.stdout.write(JSON.stringify(obj, null, 2));
With
Ln 69: process.send(obj);
It was also necessary to update the paths to the requires on line 9 and 10 of myReporter.js. I prefer this way because I'm not messing with process.stdout.write.
The last change to the code was updating the reporter path:
var Mocha = require('mocha');
process.on('message', function (message) {
const test = message.toString('utf8').replace(/\n$/,'');
new Mocha().
addFile(test).
reporter(__dirname + '/path/to/myReporter.js').
run(function(failures) {
process.exit(failures > 0 ? 1 : 0);
});
});