Tests pass:

```
$ acctests azurerm TestAccAzureRMExpressRouteCircuitAuthorization_
=== RUN   TestAccAzureRMExpressRouteCircuitAuthorization_importBasic
--- PASS: TestAccAzureRMExpressRouteCircuitAuthorization_importBasic (132.66s)
=== RUN   TestAccAzureRMExpressRouteCircuitAuthorization_basic
--- PASS: TestAccAzureRMExpressRouteCircuitAuthorization_basic (137.73s)
PASS
ok  	github.com/terraform-providers/terraform-provider-azurerm/azurerm	270.416s
```

Before these patches, this failed with:

```
* azurerm_express_route_circuit_authorization.test1: Error deleting Express Route Circuit Authorization "acctestauth12715900084028037607" (Circuit "acctest-erc-2715900084028037607" / Resource Group "acctestrg-2715900084028037607"): network.ExpressRouteCircuitAuthorizationsClient#Delete: Failure sending request: StatusCode=409 -- Original Error: failed request: autorest/azure: Service returned an error. Status=<nil> Code="AnotherOperationInProgress" Message="Another operation on this or dependent resource is in progress. To retrieve status of the operation use uri: https://management.azure.com/subscriptions/00000000-0000-0000-0000-000000000000/providers/Microsoft.Network/locations/eastus/operations/d30da8eb-3e09-480c-8844-745d73e0e8bd?api-version=2017-09-01." Details=[]
```

Now the tests pass:

```
$ acctests azurerm TestAccAzureRMExpressRouteCircuitAuthorization_multiple
=== RUN   TestAccAzureRMExpressRouteCircuitAuthorization_multiple
--- PASS: TestAccAzureRMExpressRouteCircuitAuthorization_multiple (781.75s)
PASS
ok  	github.com/terraform-providers/terraform-provider-azurerm/azurerm	781.781s
```