public void GetValidationError_All_Item_2()
        {
            // Arrange
            var propertyName1   = "Item1";
            var errorMessage1_1 = "ErrorMessage1_1.";
            var errorMessage1_2 = "ErrorMessage1_2.";
            var propertyName2   = "Item2";
            var errorMessage2_1 = "ErrorMessage2_1.";
            var errorMessage2_2 = "ErrorMessage2_2.";
            var inner           = new Dictionary <string, List <string> >
            {
                { propertyName1, new List <string> {
                      errorMessage1_1, errorMessage1_2
                  } },
                { propertyName2, new List <string> {
                      errorMessage2_1, errorMessage2_2
                  } },
            };
            var dictionary = new ValidationDictionary(inner);

            // Act
            var actual = dictionary.GetValidationError(null);

            // Assert
            var expected = new List <string>
            {
                errorMessage1_1,
                errorMessage1_2,
                errorMessage2_1,
                errorMessage2_2,
            };

            Assert.True(TestHelper.IsSameCollection(expected, actual));
        }