done() called within superagent request not working

I am creating an app with a feature to post on login. I have written the following test code in mocha. I get this error, "Error: Timeout of 2000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves". I think I made some mistake in using done(). All other assert statements have passed. Let me know where I am going wrong, or if if you need more info.

it("Login and post", function(done){
    superagent
        .post(URL_ROOT + "/register")
        .send({
            email: "posttest@test.com",
            password: "posttest"
        })
        .end(function(err, res){
            assert.ifError(err);
            var token = res.body.token;
            superagent
            .post(URL_ROOT + "/post")
            .send({
                content: "testing post",
                user: jwt.decode(token).id
            })
            .set("Authorization", "test_scheme " + token)
            .end(function(err, res){
                assert.ifError(err);
                assert.equal(res.body.post.content, "testing post");
                done();
            });
        });
});