Selenium is a protocol focused on automating the actions of a browser, and as such, it doesn't encompass the notions of a "test" that "passes" or "fails." Because of this, you need to include a section in your code that explicitly gets the status of the test, and then sends it to the Sauce Labs dashboard.
public void Cleanup()
// Gets the status of the current test
bool passed = TestContext.CurrentContext.Result.Outcome.Status == NUnit.Framework.Interfaces.TestStatus.Passed;
// Logs the result to Sauce Labs
// Terminates the remote webdriver session