howto unit test a yeoman generator - unit-testing

Question

I had a look at the official guide at http://yeoman.io/authoring/testing.html
but it left me a bit confused.
helpers.run returns a running context on which I can call methods etc.
But I'm confused how I can test if a file exists (with assert.file )
I was under the impression that helpers.run wil create the files either in memory or on the file system. But assert.file always fails.
It won't fail for files which are present on the filesystem prior to running the test.
When I run my generator (yo my-generator) I see that the files are created.
How can I test if files haven been created?
Here's my code so far which doesn't work.
I'm using jasmine for testing.
let helpers = require('yeoman-test');
let assert = require('yeoman-assert');
describe('generator:test', function () {
let path = require('path');
beforeEach(function () {
console.log(path.join(__dirname, '../generators/app'));
// The object returned acts like a promise, so return it to wait until the process is done
helpers.run(path.join(__dirname, '../generators/app'))
.withPrompts({
name: 'test',
appName: 'test',
appTitle: 'test',
apiEndpoint: 'http://localhost'
});
})
it('all config files', function () {
assert.file(#arrayOfFiles#);
});
});

Answer 1

I know this is an old question, but since it ranks quite high in Google's search results for testing Yeoman generators it seems useful to try to answer it:
Your beforeAll needs to return the Promise that helpers.run returns. Otherwise the test runner will not wait long enough before running the actual tests and the files will not be there. So your example should look like this:
let helpers = require('yeoman-test');
let assert = require('yeoman-assert');
describe('generator:test', function () {
let path = require('path');
beforeEach(function () {
return helpers.run(path.join(__dirname, '../generators/app'))
.withPrompts({
name: 'test',
appName: 'test',
appTitle: 'test',
apiEndpoint: 'http://localhost'
});
})
it('all config files', function () {
assert.file(#arrayOfFiles#);
});
});