1 files changed, 106 insertions, 0 deletions
diff --git a/activerecord/test/cases/transaction_isolation_test.rb b/activerecord/test/cases/transaction_isolation_test.rb
new file mode 100644
index 0000000000..eaafd13360
--- /dev/null
+++ b/activerecord/test/cases/transaction_isolation_test.rb
@@ -0,0 +1,106 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+
+unless ActiveRecord::Base.connection.supports_transaction_isolation?
+  class TransactionIsolationUnsupportedTest < ActiveRecord::TestCase
+    self.use_transactional_tests = false
+
+    class Tag < ActiveRecord::Base
+    end
+
+    test "setting the isolation level raises an error" do
+      assert_raises(ActiveRecord::TransactionIsolationError) do
+        Tag.transaction(isolation: :serializable) {}
+      end
+    end
+  end
+else
+  class TransactionIsolationTest < ActiveRecord::TestCase
+    self.use_transactional_tests = false
+
+    class Tag < ActiveRecord::Base
+      self.table_name = "tags"
+    end
+
+    class Tag2 < ActiveRecord::Base
+      self.table_name = "tags"
+    end
+
+    setup do
+      Tag.establish_connection :arunit
+      Tag2.establish_connection :arunit
+      Tag.destroy_all
+    end
+
+    # It is impossible to properly test read uncommitted. The SQL standard only
+    # specifies what must not happen at a certain level, not what must happen. At
+    # the read uncommitted level, there is nothing that must not happen.
+    if ActiveRecord::Base.connection.transaction_isolation_levels.include?(:read_uncommitted)
+      test "read uncommitted" do
+        Tag.transaction(isolation: :read_uncommitted) do
+          assert_equal 0, Tag.count
+          Tag2.create
+          assert_equal 1, Tag.count
+        end
+      end
+    end
+
+    # We are testing that a dirty read does not happen
+    test "read committed" do
+      Tag.transaction(isolation: :read_committed) do
+        assert_equal 0, Tag.count
+
+        Tag2.transaction do
+          Tag2.create
+          assert_equal 0, Tag.count
+        end
+      end
+
+      assert_equal 1, Tag.count
+    end
+
+    # We are testing that a nonrepeatable read does not happen
+    if ActiveRecord::Base.connection.transaction_isolation_levels.include?(:repeatable_read)
+      test "repeatable read" do
+        tag = Tag.create(name: "jon")
+
+        Tag.transaction(isolation: :repeatable_read) do
+          tag.reload
+          Tag2.find(tag.id).update(name: "emily")
+
+          tag.reload
+          assert_equal "jon", tag.name
+        end
+
+        tag.reload
+        assert_equal "emily", tag.name
+      end
+    end
+
+    # We are only testing that there are no errors because it's too hard to
+    # test serializable. Databases behave differently to enforce the serializability
+    # constraint.
+    test "serializable" do
+      Tag.transaction(isolation: :serializable) do
+        Tag.create
+      end
+    end
+
+    test "setting isolation when joining a transaction raises an error" do
+      Tag.transaction do
+        assert_raises(ActiveRecord::TransactionIsolationError) do
+          Tag.transaction(isolation: :serializable) {}
+        end
+      end
+    end
+
+    test "setting isolation when starting a nested transaction raises error" do
+      Tag.transaction do
+        assert_raises(ActiveRecord::TransactionIsolationError) do
+          Tag.transaction(requires_new: true, isolation: :serializable) {}
+        end
+      end
+    end
+  end
+end