Yep, the Failed to create COM object error is always due to licensing. As Fridjof says, you need to activate your license before trying to create any Arcobjects.
You don't need to do this if you are using mocks though. I've been testing with Visual Studio 2010 unit tests and Moq - there is very little doc available on how to use Moq with ArcObjects, but it's quite easy to figure out with the quickstart guide. You just have to remember to add every cast, call, return value, etc. to your mock. Any time you need an actual object in your test code, just use mock.Object.
For example, here's a FeatureWorkspace that has an AliasName property and you can call the OpenFeatureClass method:
// mock feature workspace object
// has AliasName and can OpenFeatureClass
var mockFeatureWorkspace = new Mock<IFeatureWorkspace>();
var mockFC = new Mock<IFeatureClass>();
mockFC.Setup(x => x.AliasName).Returns(featureClassName);
mockFeatureWorkspace.Setup(x => x.OpenFeatureClass(It.IsAny<string>())).Returns(mockFC.Object);
GeodatabaseManager.FeatureWorkspace = mockFeatureWorkspace.Object;
GeodatabaseManager and featureClassName are variables used in my test.