diff --git a/README.md b/README.md
index 3540b53..1af6530 100644
--- a/README.md
+++ b/README.md
@@ -343,6 +343,11 @@ All rspec specs and cucumber features matching the given paths will be run.
 ### `geordi unit`
 Run Test::Unit.
 
+Supports `parallel_tests`, binstubs and `bundle exec`.
+
+In order to limit processes in a parallel run, you can set an environment
+variable like this: `PARALLEL_TEST_PROCESSORS=6 geordi unit`
+
 
 ### `geordi update`
 Bring a project up to date.
diff --git a/features/unit.feature b/features/unit.feature
new file mode 100644
index 0000000..e531538
--- /dev/null
+++ b/features/unit.feature
@@ -0,0 +1,19 @@
+Feature: The unit command
+
+  Background:
+    Given a file named "test/test_helper.rb" with "enable unit tests"
+
+  Scenario: A rake binstub is used if present
+    Given a file named "bin/rake" with "binstub"
+
+    When I run `geordi unit`
+    Then the output should contain "Util.run! bin/rake, test"
+
+
+  Scenario: A rake binstub is used to run parallel tests if present
+    Given a file named "bin/rake" with "binstub"
+      And a file named "Gemfile" with "gem 'parallel_tests'"
+
+    When I run `geordi unit`
+    Then the output should contain "All unit tests at once (using parallel_tests)"
+      And the output should contain "Util.run! bin/rake, parallel:test"
diff --git a/lib/geordi/commands/unit.rb b/lib/geordi/commands/unit.rb
index a5278bb..4bc29d4 100644
--- a/lib/geordi/commands/unit.rb
+++ b/lib/geordi/commands/unit.rb
@@ -1,11 +1,23 @@
 desc 'unit', 'Run Test::Unit'
+long_desc <<-LONGDESC
+Supports `parallel_tests`, binstubs and `bundle exec`.
+
+In order to limit processes in a parallel run, you can set an environment
+variable like this: `PARALLEL_TEST_PROCESSORS=6 geordi unit`
+LONGDESC
 def unit
   if File.exist?('test/test_helper.rb')
     invoke_geordi 'bundle_install'
     invoke_geordi 'yarn_install'
 
     Interaction.announce 'Running Test::Unit'
-    Util.run!([Util.binstub_or_fallback('rake'), 'test'])
+
+    if Util.file_containing?('Gemfile', /parallel_tests/)
+      Interaction.note 'All unit tests at once (using parallel_tests)'
+      Util.run!([Util.binstub_or_fallback('rake'), 'parallel:test'], fail_message: 'Test::Unit failed.')
+    else
+      Util.run!([Util.binstub_or_fallback('rake'), 'test'], fail_message: 'Test::Unit failed.')
+    end
   else
     Interaction.note 'Test::Unit not employed.'
   end