More helpful error message when instantiating an abstract class

Calling a literal ActiveRecord::Base.new raises NoMethodError,
since it ends up calling Class.abstract_class? which does not exist.
Similarly, instantiating an actual abstract class hits the database,
when conventionally it should immediately throw NotImplementedError.

ActiveRecord::Base can't be made abstract without breaking many,
many things, so check for it separately.

1 files changed, 14 insertions, 0 deletions

diff --git a/activerecord/test/cases/base_test.rb b/activerecord/test/cases/base_test.rb
index af1845c937..8e6e462404 100644
--- a/activerecord/test/cases/base_test.rb
+++ b/activerecord/test/cases/base_test.rb
@@ -307,6 +307,20 @@ class BasicsTest < ActiveRecord::TestCase
     assert_equal("last_read", ex.errors[0].attribute)
   end
 
+  def test_initialize_abstract_class
+    e = assert_raises(NotImplementedError) do
+      FirstAbstractClass.new
+    end
+    assert_equal("FirstAbstractClass is an abstract class and can not be instantiated.", e.message)
+  end
+
+  def test_initialize_base
+    e = assert_raises(NotImplementedError) do
+      ActiveRecord::Base.new
+    end
+    assert_equal("ActiveRecord::Base is an abstract class and can not be instantiated.", e.message)
+  end
+
   def test_create_after_initialize_without_block
     cb = CustomBulb.create(:name => 'Dude')
     assert_equal('Dude', cb.name)