Add an acceptance test with a backslash in the password

This test also lets the server class create the admin user, this
abbreviates the test code a bit and increases the coverage of the
acceptance test.

Note that the explicit ordering of client and server was dropped.

spec/acceptance/server_spec.rb

@@ -85,6 +85,24 @@ class { 'mongodb::globals':
   end
 
   describe 'installation using authentication' do
+    after :all do
+      pp = <<-EOS
+        class { 'mongodb::globals':
+          #{repo_ver_param}
+        }
+        -> class { 'mongodb::server':
+          ensure         => absent,
+          package_ensure => purged,
+          service_ensure => stopped
+        }
+        -> class { 'mongodb::client':
+          ensure => purged
+        }
+      EOS
+
+      apply_manifest(pp, catch_failures: true)
+    end
+
     it 'works with no errors' do
       pp = <<-EOS
         class { 'mongodb::globals':
@@ -154,6 +172,67 @@ class { 'mongodb::globals':
     end
   end
 
+  describe 'installation using authentication with complex password' do
+    it 'works with no errors' do
+      pp = <<-EOS
+        class { 'mongodb::globals':
+        #{repo_ver_param}
+        }
+        -> class { 'mongodb::server':
+          auth           => true,
+          create_admin   => true,
+          handle_creds   => true,
+          store_creds    => true,
+          admin_username => 'admin',
+          admin_password => 'admin_\\_password',
+          restart        => true,
+        }
+        class { 'mongodb::client': }
+      EOS
+
+      apply_manifest(pp, catch_failures: true)
+      apply_manifest(pp, catch_changes: true)
+    end
+
+    describe package(package_name) do
+      it { is_expected.to be_installed }
+    end
+
+    describe file(config_file) do
+      it { is_expected.to be_file }
+    end
+
+    describe service(service_name) do
+      it { is_expected.to be_enabled }
+      it { is_expected.to be_running }
+    end
+
+    describe port(27_017) do
+      it { is_expected.to be_listening }
+    end
+
+    describe command('mongosh --quiet --eval "db.serverCmdLineOpts().ok"') do
+      its(:stderr) { is_expected.to match %r{requires authentication} }
+    end
+
+    describe file('/root/.mongoshrc.js') do
+      it { is_expected.to be_file }
+      it { is_expected.to be_owned_by 'root' }
+      it { is_expected.to be_grouped_into 'root' }
+      it { is_expected.to be_mode 600 }
+      it { is_expected.to contain 'admin.auth(\'admin\', \'admin_\\\\_password\')' }
+    end
+
+    describe command("mongosh admin --quiet --eval \"load('/root/.mongoshrc.js');EJSON.stringify(db.getUser('admin')['customData'])\"") do
+      its(:exit_status) { is_expected.to eq 0 }
+      its(:stdout) { is_expected.to match "{\"createdBy\":\"Puppet Mongodb_user['User admin on db admin']\"}\n" }
+    end
+
+    describe command('mongod --version') do
+      its(:exit_status) { is_expected.to eq 0 }
+    end
+  end
+
   describe 'uninstallation' do
     it 'uninstalls mongodb' do
       pp = <<-EOS