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How to modify test results' output in mocha.js (or another library)

I am creating a test suite that will be run by mocha. In the test, I plan on using should and chai at the very least. I am testing JSON objects. I want mocha to be silent about successful tests and I want to control what the errors look like at the end of the run. Right now, there is a lot of red text describing the JSON object and other information. What I want is to override the output.
Here is an example test for an element in the JSON object which I would import from testData.
var should = require("should");
var chai = require("chai");
var expect = chai.expect;
const testData = require("./testData");
for (t of testData.data) {
describe("This will fail", function() {
it("Should have a zipperNut",function(done) {
t.should.have.property('zipperNut');
done();
});
});
}
What I want is to see just this:
$ mocha testSuite.js
zipperNut
$
And so on for all the tests I want to run. Can I do this? Do I need to use a different library?

Mocha's output is determined by something called a "default reporter". If you want to change the output you can specify a different reporter, which is presumably available through npm or similar. To specify a new custom reporter you do this:
$ mocha --reporter my-reporter.js
Where my-reporter.js is the file containing my "reporter". For me, I just want the plain name of the failing tests, so my reporter would look like:
'use strict';
const Mocha = require('mocha');
const {
EVENT_RUN_END,
EVENT_TEST_FAIL,
} = Mocha.Runner.constants;
class MyReporter {
constructor(runner) {
const stats = runner.stats;
runner
.on(EVENT_TEST_FAIL, (test, err) => {
console.log(
`${test.title}`
);
})
.once(EVENT_RUN_END, () => {
console.log(`end: ${stats.passes}/${stats.passes + stats.failures} ok`);
});
}
}
module.exports = MyReporter;
Documentation here:
https://mochajs.org/api/tutorial-custom-reporter.html

Configuring mock-cli

I'm trying to use mock-cli to stub process.arv in mocha tests for a cli app. I want to test that a message is console.logged when an incorrect argument ("imit") is passed to process.argv (as defined by commands).
I'm trying to adapt the example from the documentation but i don't think i have set everything up correctly.
it passes when i comment out "stdin: require('../mocks/fakeInputStream'), // Hook up a fake input stream" though i know it's not working correctly
it fails with TypeError: sourceStream.on is not a function when run as described below
Can someone see what I'm missing?
/index.js
var commands = ['init'];
function getGitHeadArgs() {
return process.argv.slice(2, process.argv.length);
}
if (getGitHeadArgs().length) {
if (!commands.includes(getGitHeadArgs()[0])) {
console.log("Silly Githead! That's not a githead command");
}
eval(getGitHeadArgs()[0])();
} else {
console.log("You didn't tell githead to do anything!");
}
/testIndex.js
var assert = require('assert');
var index = require('../index.js');
var mockCli = require("mock-cli");
describe("incorrect argument", function() {
it("imit throws an error if an invalid command is raised", function() {
var argv = ['node', '../index.js', 'imit']; // Fake argv
var stdio = {
stdin: require('../mocks/fakeInputStream'), // Hook up a fake input stream
stdout: process.stdout, // Display the captured output in the main console
stderr: process.stderr // Display the captured error output in the main console
};
var kill = mockCli(argv, stdio, function onProcessComplete(error, result) {
var exitCode = result.code; // Process exit code
var stdout = result.stdout; // UTF-8 string contents of process.stdout
var stderr = result.stderr; // UTF-8 string contents of process.stderr
assert.equal(exitCode, 0);
assert.equal(stdout, "Silly Githead! That's not a githead command\n");
assert.equal(stderr, '');
});
// Execute the CLI task
require('../index.js');
// Kill the task if still running after one second
setTimeout(kill, 1000);
});

Is ../mocks/fakeInputStream a valid path?
Is the object at ../mocks/fakeInputStream a valid instance of ReadableStream?
The source code is avalible at GitHub.
Make sure you meet the requirements for the captureStdin(sourceStream, callback) function.
The module uses that function to capture your fakeInputStream and pipe it into a captureStream.

Mocking console.log()/Any Other Function in MOCHA testing framework

I am writing test cases for NODE JS API. But wherever console.log() is there in routes or services of NODE JS File, it gets printed to CLI. Is there a way to mock these so that these won't get printed in CLI.
I have explored couple of libraries like Sinon, Stub for mocking. But couldn't grasp the working of those libraries.

You can override function entirely: console.log = function () {}.

You should not try to mock console.log itself, a better approach is for your node modules to take a logging object. This allows you to provide an alternative (ie. a mock) during testing. For example:
<my_logger.js>
module.exports = {
err: function(message) {
console.log(message);
}
}
<my_module.js>
var DefaultLogger = require('my_logger.js');
module.exports = function(logger) {
this.log = logger || DefaultLogger;
// Other setup goes here
};
module.exports.prototype.myMethod = function() {
this.log.err('Error message.');
};
<my_module_test.js>
var MyModule = require('my_module.js');
describe('Test Example', function() {
var log_mock = { err: function(msg) {} };
it('Should not output anything.', function() {
var obj = new MyModule(log_mock);
obj.myMethod();
});
});
The code here I've simplified, as the actual test isn't the reason for the example. Merely the insertion of alternative logging.
If you have a large codebase with lots of console.log calls, it is better to simply update the code as you add tests for each method. Making your logging pluggable in this way makes your code easier and more receptive to testing. Also, there are many logging frameworks available for node. console.log is fine during development when you just want to dump out something to see what's going on. But, if possible, try to avoid using it as your logging solution.

I could not find a solution which only hides the console.log calls in the module to be tested, and mocks none of the calls of the testing framework (mocha/chai in my case).
I came up with using a copy of console in the app code:
/* console.js */
module.exports = console;
/* app.js */
const console = require('./console');
console.log("I'm hidden in the tests");
/* app.spec.js */
const mockery = require('mockery');
var app;
before(() => {
// Mock console
var consoleMock = {
log: () => {}
}
mockery.registerMock('./console', consoleMock);
// Require test module after mocking
app = require('./app');
});
after(() => {
mockery.deregisterAll();
mockery.disable();
});
it('works', () => {});

You could do something along the lines of adding these before/after blocks to your tests, but the issue is that mocha actually uses console.log to print the pretty messages about the results of the test, so you would lose those
describe('Test Name', function() {
var originalLog;
beforeEach(function() {
originalLog = console.log;
console.log = function () {};
});
// test code here
afterEach(function() {
console.log = originalLog;
})
})
The problem is that your output would just look like
Test Name
X passing (Yms)
Without any intermediate text

Using babel, how can I append some code to the top of every file?

My goal is to fake out getting some requirejs code working via babel. I've found that if I add the following: if (typeof define !== "function") { var define = require("amdefine")(module); } to the top of every file while running in nodejs things seem to work out.
Here is some code I wrote, which I thought would work or nearly work:
function injectDefine(babel) {
var header = 'if (typeof define !== "function") { var define = require("amdefine")(module); }';
return new babel.Plugin('amdefine', {
visitor: {
Program: {
enter: function(path, file) {
path.unshiftContainer(
'body',
babel.types.expressionStatement(
babel.types.stringLiteral(header)
)
);
},
},
},
});
}
require('babel-core/register')({
stage: 0,
plugins: [{transformer: injectDefine}],
});
require('../components/button');
The components/button file is just me trying to test that some file can load.
Other notes: I'm using babel 5, and I can't upgrade right now. I also can't use a .babelrc very easily right now.

Tip 1: the environment variable BABEL_DISABLE_CACHE=1 is needed if you are doing heavy testing of plugins. If you had a script that you ran like npm run unit you may instead want to run like BABEL_DISABLE_CACHE=1 npm run unit while testing your plugin.
Tip 2: babel.parse will give you a full program out of some source. The easiest thing you could do is babel.parse(header).program.body[0].
The following ended up working:
function injectDefine(babel) {
var header = 'if (typeof define !== "function") { var define = require("amdefine")(module); }';
return new babel.Plugin('amdefine', {
visitor: {
Program: {
enter: function(node, parent) {
node.body.unshift(
babel.parse(header).program.body[0]
);
},
},
},
});
}
require('babel-core/register')({
cache: false,
stage: 0,
plugins: [injectDefine],
});

At this stage, a cleaner solution can be to use #babel/traverse and #babel/types.
Let's suppose you want to append a comment to the top of every file, you could use some code like the following:
// Import the required modules
import * as t from "#babel/types";
import traverse from "#babel/traverse";
// Get your ast (for this, you can use #babel/parser)
// Traverse your ast
traverse(ast, {
// When the current node is the Program node (so the main node)
Program(path) {
// Insert at the beginning a string "Hello World" --> not valid JS code
path.unshiftContainer('body', t.stringLiteral("Hello World"));
}
});

Can I mock console in NodeJs?

In my JS test, I need to check if the console.info is called. That's why I want to mock console. However, it seems that the console variable cannot be assigned with a different object. Did I make any mistake?
Here is the code I used:
var oldConsole = console;
var infoContent;
console = {
info: function(content) {
infoContent = content;
}
};
game.process('a command');
infoContent.should.equal('a command is processed');
console = oldConsole;

You can use rewire to replace the whole of console to silence it, or to inject a mock. I use deride but sinon would also work.
var rewire = require('rewire');
var deride = require('deride');
var Game = rewire('../lib/game');
describe('game testing', function() {
var stubConsole, game;
beforeEach(function() {
stubConsole = deride.stub(['info']);
stubConsole.setup.info.toReturn();
Game.__set__({
console: stubConsole
});
game = new Game();
});
it('logs info messages', function() {
game.process('a command');
stubConsole.expect.info.called.withArgs(['a command is processed']);
});
});

I find the solution. I can change the method info of console.
console.info = function(content) {
infoContent = content;
};
The question is now why console object itself cannot be reassigned?

you can use sinon npm to count the call to a function :
it("calls the original function only once", function () {
var callback = sinon.spy();
var proxy = once(callback);
proxy();
proxy();
assert(callback.calledOnce);
// ...or:
// assert.equals(callback.callCount, 1);
});
You can find the docs here : sinonjs.org

I thought I had the same problem and my solution was using this std-mocks module:
https://github.com/neoziro/std-mocks
This has the advantage of not taking over the global "console" but allows you to see what gets logged to the stdout / stderr. This solves the problem in a different way than the question was explicitly looking for; however I believe it is a good answer for the problem the question implies and may be useful for others.
const stdMocks = require('std-mocks');
stdMocks.use(); console.log('test'); stdMocks.restore();
// => undefined [nothing gets output, stdout intercepted]
const logged = stdMocks.flush();
console.log(logged)
// => { stdout: [ 'test\n' ], stderr: [] }