⚠️ "Use assert_nil if expecting nil. This will fail in MT6."

These are followups for 307065f959,
but TBH I'm personally not very much confortable with this style.
Maybe we could override assert_equal in our test_helper not to warn?

actionpack/test/controller/parameters/parameters_permit_test.rb

@@ -66,12 +66,20 @@ class ParametersPermitTest < ActiveSupport::TestCase
     values.each do |value|
       params = ActionController::Parameters.new(id: value)
       permitted = params.permit(:id)
-      assert_equal value, permitted[:id]
+      if value.nil?
+        assert_nil permitted[:id]
+      else
+        assert_equal value, permitted[:id]
+      end
 
       @struct_fields.each do |sf|
         params = ActionController::Parameters.new(sf => value)
         permitted = params.permit(:sf)
-        assert_equal value, permitted[sf]
+        if value.nil?
+          assert_nil permitted[sf]
+        else
+          assert_equal value, permitted[sf]
+        end
       end
     end
   end

actionpack/test/controller/request/test_request_test.rb

@@ -21,16 +21,20 @@ class ActionController::TestRequestTest < ActionController::TestCase
                  @request.get_header("CONTENT_LENGTH"))
   end
 
-  ActionDispatch::Session::AbstractStore::DEFAULT_OPTIONS.each_key do |option|
-    test "rack default session options #{option} exists in session options and is default" do
-      assert_equal(ActionDispatch::Session::AbstractStore::DEFAULT_OPTIONS[option],
-                   @request.session_options[option],
-                   "Missing rack session default option #{option} in request.session_options")
+  ActionDispatch::Session::AbstractStore::DEFAULT_OPTIONS.each_pair do |key, value|
+    test "rack default session options #{key} exists in session options and is default" do
+      if value.nil?
+        assert_nil(@request.session_options[key],
+                   "Missing rack session default option #{key} in request.session_options")
+      else
+        assert_equal(value, @request.session_options[key],
+                     "Missing rack session default option #{key} in request.session_options")
+      end
     end
 
-    test "rack default session options #{option} exists in session options" do
-      assert(@request.session_options.has_key?(option),
-                   "Missing rack session option #{option} in request.session_options")
+    test "rack default session options #{key} exists in session options" do
+      assert(@request.session_options.has_key?(key),
+                   "Missing rack session option #{key} in request.session_options")
     end
   end
 end

actionview/test/template/erb_util_test.rb

@@ -51,7 +51,12 @@ class ErbUtilTest < ActiveSupport::TestCase
 
   def test_json_escape_does_not_alter_json_string_meaning
     JSON_ESCAPE_TEST_CASES.each do |(raw, _)|
-      assert_equal ActiveSupport::JSON.decode(raw), ActiveSupport::JSON.decode(json_escape(raw))
+      expected = ActiveSupport::JSON.decode(raw)
+      if expected.nil?
+        assert_nil ActiveSupport::JSON.decode(json_escape(raw))
+      else
+        assert_equal expected, ActiveSupport::JSON.decode(json_escape(raw))
+      end
     end
   end
 

activerecord/test/cases/adapters/sqlite3/copy_table_test.rb

@@ -41,8 +41,8 @@ class CopyTableTest < ActiveRecord::SQLite3TestCase
     test_copy_table("comments", "comments_with_index") do
       @connection.add_index("comments_with_index", ["post_id", "type"])
       test_copy_table("comments_with_index", "comments_with_index2") do
-        assert_equal table_indexes_without_name("comments_with_index"),
-                     table_indexes_without_name("comments_with_index2")
+        assert_nil table_indexes_without_name("comments_with_index")
+        assert_nil table_indexes_without_name("comments_with_index2")
       end
     end
   end
@@ -59,7 +59,8 @@ class CopyTableTest < ActiveRecord::SQLite3TestCase
       copied_id = @connection.columns("goofy_string_id2").detect { |col| col.name == "id" }
       assert_equal original_id.type, copied_id.type
       assert_equal original_id.sql_type, copied_id.sql_type
-      assert_equal original_id.limit, copied_id.limit
+      assert_nil original_id.limit
+      assert_nil copied_id.limit
     end
   end
 

activerecord/test/cases/associations/eager_test.rb

@@ -933,7 +933,11 @@ class EagerAssociationTest < ActiveRecord::TestCase
     d2 = find_all_ordered(Firm, :account)
     d1.each_index do |i|
       assert_equal(d1[i], d2[i])
-      assert_equal(d1[i].account, d2[i].account)
+      if d1[i].account.nil?
+        assert_nil(d2[i].account)
+      else
+        assert_equal(d1[i].account, d2[i].account)
+      end
     end
   end
 
@@ -943,7 +947,13 @@ class EagerAssociationTest < ActiveRecord::TestCase
     d2 = find_all_ordered(Client, firm_types)
     d1.each_index do |i|
       assert_equal(d1[i], d2[i])
-      firm_types.each { |type| assert_equal(d1[i].send(type), d2[i].send(type)) }
+      firm_types.each do |type|
+        if (expected = d1[i].send(type)).nil?
+          assert_nil(d2[i].send(type))
+        else
+          assert_equal(expected, d2[i].send(type))
+        end
+      end
     end
   end
   def test_eager_with_valid_association_as_string_not_symbol

activerecord/test/cases/associations/inverse_associations_test.rb

@@ -443,7 +443,7 @@ class InverseHasManyTests < ActiveRecord::TestCase
     assert man.equal?(man.interests.first.man), "Two inverses should lead back to the same object that was originally held"
     assert man.equal?(man.interests.find(interest.id).man), "Two inversions should lead back to the same object that was originally held"
 
-    assert_equal man.name, man.interests.find(interest.id).man.name, "The name of the man should match before the name is changed"
+    assert_nil man.interests.find(interest.id).man.name, "The name of the man should match before the name is changed"
     man.name = "Ben Bitdiddle"
     assert_equal man.name, man.interests.find(interest.id).man.name, "The name of the man should match after the parent name is changed"
     man.interests.find(interest.id).man.name = "Alyssa P. Hacker"

activerecord/test/cases/transactions_test.rb

@@ -279,7 +279,11 @@ class TransactionTest < ActiveRecord::TestCase
       e = assert_raises(RuntimeError) { new_topic.save }
       assert_equal "Make the transaction rollback", e.message
       assert_equal new_record_snapshot, !new_topic.persisted?, "The topic should have its old persisted value"
-      assert_equal id_snapshot, new_topic.id, "The topic should have its old id"
+      if id_snapshot.nil?
+        assert_nil new_topic.id, "The topic should have its old id"
+      else
+        assert_equal id_snapshot, new_topic.id, "The topic should have its old id"
+      end
       assert_equal id_present, new_topic.has_attribute?(Topic.primary_key)
     end
   end