Sinon + Promise

I'm trying to test app in NodeJS. For tests I'm using MochaJS, sinon, sinon-mongoose, sinon-as-promised and ShouldJS. I wrote a test and I had a problem with mock. Situation does look like this: API:

app.post('/api/admin/content', function (req, res) {
        var contents = [];
        var promise1 = new Promise(function(resolves, rejects){
            content.find().exec(function(err, contentRecord){
                if (err) return rejects();
            return resolves(contentRecord);
        })
    }).then(function(data){
        contents.push(data);
    });

... 

add here adding a new content 

...

    var promise2 = new Promise(function(resolves, rejects){
        content.find().exec(function(err, contentRecord){
            if (err) return rejects();

            return resolves(contentRecord);
        })
    }).then(function(data){
        contents.push(data);
    });

    Promise.all([promise1, promise2]).then(function(){
        if (contents.length > 1) {
            return res.send(contents);
        } else {
            return res.status(400).send();
        }
    });
});

TEST:

describe('/routes/admin/content', function () {
    it('get_all_contents', function(done){
        contentMock.expects('find').chain('exec').withArgs(sinon.match.any).yields(null, [{"L":1}]);
        request(server)
            .json()
            .base('http://localhost:8889')
            .post('/api/admin/content')
            .expectStatus(200)
            .end(function (err, req, body) {
                if (err) throw err;
                body.should.not.be.empty();
                done();
            });
    })
});

While the first Promise is working as expected, the second one, simply fails (there is an error with exceeding time). I even found a solution for this (though it is hardly a solution), and its about removing this line:

contentMock.expects('find').chain('exec').withArgs(sinon.match.any).yields(null, [{"L":1}]);

The problem only occurs in test, while application works pretty fine with that api as it is.

How to properly write a mock over here? Cause I'm expecting that to be the case.