How can I dynamically generate test cases in javascript/node?

Question

The nose testing framework (for python) supports dynamically generating test cases at run-time (the following, from the documentation, results in five distinct test cases):

def test_evens():
    for i in range(0, 5):
        yield check_even, i, i*3

def check_even(n, nn):
    assert n % 2 == 0 or nn % 2 == 0

How can I achieve this result using javascript frameworks such as mocha or qunit? (I am not attached to any particular framework at this point.)

My use-case is writing a test runner to monitor several items on an external server. I would provide a list of resource URLs. Each test attempts to poll that resource and returns success or failure depending on what it finds. I have a prototype built in python (using nose) but would like to implement in node.js if I can. Eventually, this would be included in a CI setup.

Answer 1

Yes you can dynamically created test suites with cases using Mocha. I have installed mocha globally npm install -g mocha and I use should.

var should = require('should');

var foo = 'bar';

['nl', 'fr', 'de'].forEach(function(arrElement) {
  describe(arrElement + ' suite', function() {
    it('This thing should behave like this', function(done) {
      foo.should.be.a.String();
      done();
    });
    it('That thing should behave like that', function(done) {
      foo.should.have.length(3);
      done();
    });
  });
});

Answer 2

If you want to dynamically create It() tests using data obtained asynchronously, you can (ab)use the before() hook with a placeholder It() test to ensure mocha waits until before() is run. Here's the example from my answer to a related question, for convenience:

before(function () {
    console.log('Let the abuse begin...');
    return promiseFn().
        then(function (testSuite) {
            describe('here are some dynamic It() tests', function () {
                testSuite.specs.forEach(function (spec) {
                    it(spec.description, function () {
                        var actualResult = runMyTest(spec);
                        assert.equal(actualResult, spec.expectedResult);
                    });
                });
            });
        });
});

it('This is a required placeholder to allow before() to work', function () {
    console.log('Mocha should not require this hack IMHO');
});

Answer 3

With Mocha 1.21.4, you can create suite/test at runtime in following way.

require('chai').should()

Mocha = require 'mocha'
Test = Mocha.Test
Suite = Mocha.Suite


mocha = new Mocha
suite = Suite.create mocha.suite, 'I am a dynamic suite'
suite.addTest new Test 'I am a dynamic test', ->
  true.should.equal true

mocha.run () ->
  console.log("done")

See https://gist.github.com/cybertk/fff8992e12a7655157ed for more details

Answer 4

It's worth noting that in addition to the accepted answer above, mocha's docs now include an example of how to achieve this. I've reproduced it below for posterity.

var assert = require('assert');

function add() {
  return Array.prototype.slice.call(arguments).reduce(function(prev, curr) {
    return prev + curr;
  }, 0);
}

describe('add()', function() {
  var tests = [
    {args: [1, 2],       expected: 3},
    {args: [1, 2, 3],    expected: 6},
    {args: [1, 2, 3, 4], expected: 10}
  ];

  tests.forEach(function(test) {
    it('correctly adds ' + test.args.length + ' args', function() {
      var res = add.apply(null, test.args);
      assert.equal(res, test.expected);
    });
  });
});

Answer 5

Yep! Brilliant advice from Quanlong!

Here is my example of dynamic test generation with Node's readline module:

const Mocha = require('mocha');
var Test = Mocha.Test;
var Suite = Mocha.Suite;

var mocha = new Mocha();
var suite = Suite.create(mocha.suite, 'My test suite with dynamic test cases');

lineReader
    .on('line', function (line) {
        suite.addTest(new Test(line, function () {
            return true;
        }));
    })
    .on('close', function () {
        mocha.run();
    });

Answer 6

I like @rob3c's answer, but tried to simplify it a bit:

describe("Master test suite", function () {
  before(async function () {
    const rows = await mySQLQuery();

    describe(`Testing ${rows.length} rows`, function () {
      rows.forEach(function (row, index) {
        it(`Test row ${index}`, async function() {
          console.log("your row assertions go here")
        });
      });
    });
  });


  it("stub", async function(){})  // this is important!
});

Answer 7

You can accomplish this by updating the tests property manually after the response is returned from the async method:

describe(`sometest`, function() {
  let results = null
  before(async () => {
    results = await someAsyncMethod();
    results.forEach((result, index) => {
      // to hold on to the new dynamic tests
      const newTest = it(result.name || `test ${index}`, () => {
        // do something here in test
      });
      // update the test objects before the main tests run
      this.tests.push(newTest);
    });
  });

  it(`sometest`, () => {
    expect(results.length).toBeGreaterThan(2);
  });

});

This doesn't use dynamic describes etc, just updates the current describe block before the main tests run!