suggested test cases:

describe("set value", function(){
  let stuff = {};
  it ("set value", function(){
      namespace(stuff, 'moreStuff.name', 'the stuff');
      Test.assertSimilar(stuff, {moreStuff: {name: 'the stuff'}});
  });
});

describe("get value", function(){
  let stuff = {moreStuff: {name: 'the stuff'}};
  it ("valid path", function(){
      Test.assertEquals(namespace(stuff, 'moreStuff.name'), 'the stuff');
  });
  
  it ("invalid path", function(){
      Test.assertEquals(namespace(stuff, 'otherStuff.id'), undefined);
  });
});