Rewrite hm:t#create tests using assert_no_difference and assert_difference

activerecord/test/cases/associations/has_many_through_associations_test.rb

@@ -180,27 +180,23 @@ def test_create_on_new_record
   end
 
   def test_associate_with_create_and_invalid_options
-    peeps = companies(:first_firm).developers.count
-    assert_nothing_raised { companies(:first_firm).developers.create(:name => '0') }
-    assert_equal peeps, companies(:first_firm).developers.count
+    firm = companies(:first_firm)
+    assert_no_difference('firm.developers.count') { assert_nothing_raised { firm.developers.create(:name => '0') } }
   end
 
   def test_associate_with_create_and_valid_options
-    peeps = companies(:first_firm).developers.count
-    assert_nothing_raised { companies(:first_firm).developers.create(:name => 'developer') }
-    assert_equal peeps + 1, companies(:first_firm).developers.count
+    firm = companies(:first_firm)
+    assert_difference('firm.developers.count', 1) { firm.developers.create(:name => 'developer') }
   end
 
   def test_associate_with_create_bang_and_invalid_options
-    peeps = companies(:first_firm).developers.count
-    assert_raises(ActiveRecord::RecordInvalid) { companies(:first_firm).developers.create!(:name => '0') }
-    assert_equal peeps, companies(:first_firm).developers.count
+    firm = companies(:first_firm)
+    assert_no_difference('firm.developers.count') { assert_raises(ActiveRecord::RecordInvalid) { firm.developers.create!(:name => '0') } }
   end
 
   def test_associate_with_create_bang_and_valid_options
-    peeps = companies(:first_firm).developers.count
-    assert_nothing_raised { companies(:first_firm).developers.create!(:name => 'developer') }
-    assert_equal peeps + 1, companies(:first_firm).developers.count
+    firm = companies(:first_firm)
+    assert_difference('firm.developers.count', 1) { firm.developers.create!(:name => 'developer') }
   end
 
   def test_clear_associations