How to Construct IdentityResult With Success == true
To make the Succeeded property equal to True use either of these examples:
return IdentityResult.Success;
IdentityResult result = IdentityResult.Success;
Would the static IdentityResult.Success property work? http://msdn.microsoft.com/en-us/library/microsoft.aspnet.identity.identityresult.success(v=vs.108).aspx
Edit: To add some more detail, it seems what you want to do is get your mocked CreateAsync to return an IdentityResult where Suceeded is true. For that I would just return IdentityResult.Success from your mock. There's shouldn't be a need to mock the IdentityResult itself.
Example: How to setup a service that returns Successful identity result.
applicationUserManagerMock.Setup(s =>
s.CreateAsync(It.IsAny<ApplicationUser>(), It.IsAny<string>())
).ReturnsAsync(IdentityResult.Success);