Use `safe_constantize`.

Fixes https://github.com/rails/rails/issues/9933.

activesupport/lib/active_support/testing/constant_lookup.rb

@@ -36,12 +36,8 @@ module ActiveSupport
           while names.size > 0 do
             names.last.sub!(/Test$/, "")
             begin
-              constant = names.join("::").constantize
+              constant = names.join("::").safe_constantize
               break(constant) if yield(constant)
-            rescue NoMethodError # subclass of NameError
-              raise
-            rescue NameError
-              # Constant wasn't found, move on
             ensure
               names.pop
             end

activesupport/test/constantize_test_cases.rb

@@ -1,3 +1,5 @@
+require 'dependencies_test_helpers'
+
 module Ace
   module Base
     class Case
@@ -23,6 +25,8 @@ class Object
 end
 
 module ConstantizeTestCases
+  include DependenciesTestHelpers
+
   def run_constantize_tests_on
     assert_equal Ace::Base::Case, yield("Ace::Base::Case")
     assert_equal Ace::Base::Case, yield("::Ace::Base::Case")
@@ -56,6 +60,19 @@ module ConstantizeTestCases
     assert_raises(NameError) { yield("Ace::Gas::ConstantizeTestCases") }
     assert_raises(NameError) { yield("") }
     assert_raises(NameError) { yield("::") }
+    assert_raises(NameError) { yield("Ace::gas") }
+
+    assert_raises(NameError) do
+      with_autoloading_fixtures do
+        yield("RaisesNameError")
+      end
+    end
+
+    assert_raises(NoMethodError) do
+      with_autoloading_fixtures do
+        yield("RaisesNoMethodError")
+      end
+    end
   end
 
   def run_safe_constantize_tests_on
@@ -82,5 +99,18 @@ module ConstantizeTestCases
     assert_nil yield("Ace::Gas::Base")
     assert_nil yield("Ace::Gas::ConstantizeTestCases")
     assert_nil yield("#<Class:0x7b8b718b>::Nested_1")
+    assert_nil yield("Ace::gas")
+
+    assert_raises(NameError) do
+      with_autoloading_fixtures do
+        yield("RaisesNameError")
+      end
+    end
+
+    assert_raises(NoMethodError) do
+      with_autoloading_fixtures do
+        yield("RaisesNoMethodError")
+      end
+    end
   end
 end

activesupport/test/dependencies_test.rb

@@ -888,6 +888,8 @@ class DependenciesTest < ActiveSupport::TestCase
         assert_raise(NameError) { assert_equal 123, ::RaisesNameError::FooBarBaz }
       end
     end
+  ensure
+    remove_constants(:RaisesNameError)
   end
 
   def test_autoload_doesnt_shadow_name_error

activesupport/test/testing/constant_lookup_test.rb

@@ -65,4 +65,12 @@ class ConstantLookupTest < ActiveSupport::TestCase
       }
     }
   end
+
+  def test_does_not_swallow_exception_on_no_name_error_within_constant
+    assert_raises(NameError) do
+      with_autoloading_fixtures do
+        self.class.determine_constant_from_test_name('RaisesNameError')
+      end
+    end
+  end
 end