Ensure variable names exist in method

plugins/providers/docker/action/prepare_networks.rb

@@ -42,12 +42,13 @@ module VagrantPlugins
         # Validates that a network name exists. If it does not
         # exist, an exception is raised.
         #
-        # @param [String] name Name of existing network
+        # @param [String] network_name Name of existing network
+        # @param [Hash] env Local call env
         # @return [Boolean]
-        def validate_network_name!(name)
+        def validate_network_name!(network_name, env)
           if !env[:machine].provider.driver.existing_named_network?(network_name)
             raise Errors::NetworkNameUndefined,
-              network_name: name
+              network_name: network_name
           end
           true
         end
@@ -83,7 +84,7 @@ module VagrantPlugins
         # @param [Hash] env Local call env
         # @return [String, Hash] Network name and updated network_options
         def process_private_network(root_options, network_options, env)
-          if root_options[:name] && validate_network_name!(root_options[:name])
+          if root_options[:name] && validate_network_name!(root_options[:name], env)
             network_name = root_options[:name]
           end
 
@@ -150,7 +151,7 @@ module VagrantPlugins
         # @param [Hash] env Local call env
         # @return [String, Hash] Network name and updated network_options
         def process_public_network(root_options, net_options, env)
-          if root_options[:name] && validate_network_name!(root_options[:name])
+          if root_options[:name] && validate_network_name!(root_options[:name], env)
             network_name = root_options[:name]
           end
           if !network_name

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

@@ -105,7 +105,6 @@ describe VagrantPlugins::DockerProvider::Action::PrepareNetworks do
       expect(driver).to receive(:create_network).
         with("vagrant_network_2a02:6b8:b010:9020:1::/80", ["--ipv6", "--subnet", "2a02:6b8:b010:9020:1::/80"])
 
-
       subject.call(env)
 
       expect(env[:docker_connects]).to eq({0=>"vagrant_network_172.20.128.0/24", 1=>"vagrant_network_public_wlp4s0", 2=>"vagrant_network_2a02:6b8:b010:9020:1::/80"})
@@ -193,10 +192,22 @@ describe VagrantPlugins::DockerProvider::Action::PrepareNetworks do
     end
   end
 
-  describe "#list_interfaces" do
-  end
-
   describe "#validate_network_name!" do
+    let(:netname) { "vagrant_network" }
+
+    it "returns true if name exists" do
+      allow(driver).to receive(:existing_named_network?).with(netname).
+        and_return(true)
+
+      expect(subject.validate_network_name!(netname, env)).to be_truthy
+    end
+
+    it "raises an error if name does not exist" do
+      allow(driver).to receive(:existing_named_network?).with(netname).
+        and_return(false)
+
+      expect{subject.validate_network_name!(netname, env)}.to raise_error(VagrantPlugins::DockerProvider::Errors::NetworkNameUndefined)
+    end
   end
 
   describe "#validate_network_configuration!" do