fix Authenticator unit test

authenticator/src/test/java/com/amplifyframework/ui/authenticator/AuthenticatorViewModelTest.kt

@@ -50,6 +50,7 @@ class AuthenticatorViewModelTest {
 
     @Test
     fun `start only executes once`() = runTest {
+        coEvery {authProvider.fetchAuthSession()}.returns(AmplifyResult.Error(mockAuthException()))
         viewModel.start(mockAuthConfiguration())
         viewModel.start(mockAuthConfiguration())
         advanceUntilIdle()