Add edge test cases for integer and string types

activemodel/test/cases/type/integer_test.rb

@@ -50,6 +50,13 @@ class IntegerTest < ActiveModel::TestCase
         assert_equal 7200, type.cast(2.hours)
       end
 
+      test "casting empty string" do
+        type = Type::Integer.new
+        assert_nil type.cast("")
+        assert_nil type.serialize("")
+        assert_equal 0, type.deserialize("")
+      end
+
       test "changed?" do
         type = Type::Integer.new
 

activemodel/test/cases/type/string_test.rb

@@ -12,6 +12,14 @@ class StringTest < ActiveModel::TestCase
         assert_equal "123", type.cast(123)
       end
 
+      test "type casting for database" do
+        type = Type::String.new
+        object, array, hash = Object.new, [true], { a: :b }
+        assert_equal object, type.serialize(object)
+        assert_equal array, type.serialize(array)
+        assert_equal hash, type.serialize(hash)
+      end
+
       test "cast strings are mutable" do
         type = Type::String.new