Something like this would test DeleteVendorBrief, for example.
Mock<IVendorBriefRepository> mock = new Mock<IVendorBriefRepository>();
VendorBriefController controller = new VendorBriefController(mock.Object);
VendorBrief brief = new VendorBrief();
controller.DeleteVendorBrief(brief);
mock.Verify(f=>f.DeleteVendorBrief(brief));
mock.Verify(f=>f.SaveChanges());