Introduce Module#concerning

A natural, low-ceremony way to separate responsibilities within a class.

Imported from https://github.com/37signals/concerning#readme

1 files changed, 35 insertions, 0 deletions

diff --git a/activesupport/test/core_ext/module/concerning_test.rb b/activesupport/test/core_ext/module/concerning_test.rb
new file mode 100644
index 0000000000..c6863b24a4
--- /dev/null
+++ b/activesupport/test/core_ext/module/concerning_test.rb
@@ -0,0 +1,35 @@
+require 'abstract_unit'
+require 'active_support/core_ext/module/concerning'
+
+class ConcerningTest < ActiveSupport::TestCase
+  def test_concern_shortcut_creates_a_module_but_doesnt_include_it
+    mod = Module.new { concern(:Foo) { } }
+    assert_kind_of Module, mod::Foo
+    assert mod::Foo.respond_to?(:included)
+    assert !mod.ancestors.include?(mod::Foo), mod.ancestors.inspect
+  end
+
+  def test_concern_creates_a_module_extended_with_active_support_concern
+    klass = Class.new do
+      concern :Foo do
+        included { @foo = 1 }
+        def should_be_public; end
+      end
+    end
+
+    # Declares a concern but doesn't include it
+    assert_kind_of Module, klass::Foo
+    assert !klass.ancestors.include?(klass::Foo), klass.ancestors.inspect
+
+    # Public method visibility by default
+    assert klass::Foo.public_instance_methods.map(&:to_s).include?('should_be_public')
+
+    # Calls included hook
+    assert_equal 1, Class.new { include klass::Foo }.instance_variable_get('@foo')
+  end
+
+  def test_concerning_declares_a_concern_and_includes_it_immediately
+    klass = Class.new { concerning(:Foo) { } }
+    assert klass.ancestors.include?(klass::Foo), klass.ancestors.inspect
+  end
+end