Add pushgateway spec test

spec/classes/pushgateway_spec.rb

@@ -0,0 +1,25 @@
+require 'spec_helper'
+
+describe 'prometheus::pushgateway' do
+  on_supported_os.each do |os, facts|
+    context "on #{os}" do
+      let(:facts) do
+        facts
+      end
+
+      context 'with version specified' do
+        let(:params) do
+          {
+              version: '0.4.0',
+              arch: 'amd64',
+              os: 'linux'
+          }
+        end
+
+        describe 'install correct binary' do
+          it { is_expected.to contain_file('/usr/local/bin/pushgateway').with('target' => '/opt/pushgateway-0.4.0.linux-amd64/pushgateway') }
+        end
+      end
+    end
+  end
+end