Add public network tests for docker provider

plugins/providers/docker/errors.rb

@@ -69,6 +69,10 @@ module VagrantPlugins
         error_key(:network_name_undefined)
       end
 
+      class NetworkNoInterfaces < DockerError
+        error_key(:network_no_interfaces)
+      end
+
       class PackageNotSupported < DockerError
         error_key(:package_not_supported)
       end

templates/locales/providers_docker.yml

@@ -252,6 +252,9 @@ en:
         The Docker provider was unable to configure networking using the
         provided network name `%{network_name}`. Please ensure the network
         name is correct and exists, then try again.
+      network_no_interfaces: |-
+        The Docker provider was unable to list any available interfaces to bridge
+        the public network with.
       network_subnet_invalid: |-
         The configured network subnet is not valid for the defined network.
         Please update the network settings and try again.

test/unit/plugins/providers/docker/action/prepare_networks_test.rb

@@ -281,6 +281,21 @@ describe VagrantPlugins::DockerProvider::Action::PrepareNetworks do
   end
 
   describe "#process_public_network" do
+    let(:options) { {:ip=>"172.30.130.2", :subnet=>"172.30.0.0/16", :driver=>"bridge", :id=>"30e017d5-488f-5a2f-a3ke-k8dce8246b60"} }
+
+    it "raises an error if there are no network interfaces" do
+      expect(subject).to receive(:list_interfaces).and_return([])
+
+      expect{subject.process_public_network(options, {}, env)}.
+        to raise_error(VagrantPlugins::DockerProvider::Errors::NetworkNoInterfaces)
+    end
+
+    it "generates a network name and configuration" do
+      allow(machine.ui).to receive(:ask).and_return("1")
+
+      network_name, network_options = subject.process_public_network(options, {}, env)
+      expect(network_name).to eq("vagrant_network_public")
+    end
   end
 
   describe "#request_public_gateway" do