Question

I was trying to write a piece of code for converting a list of strings to a list of ints
I got the List<int> list = listOfStr.ConvertAll<int>(delegate(string s) { return ConvertStringToInt(s); }); line from ConvertAll .

    public static List<int> ConvertListOfStringToListOfInt(List<string> listOfStr)
    {
        List<int> list = listOfStr.ConvertAll<int>(delegate(string s) { return ConvertStringToInt(s); });

        return list;
    }
    /// <summary>
    /// converts the given str to integer
    /// </summary>
    /// <param name="str">string to be converted</param>
    /// <returns>returns the int value of the given string</returns>
    public static int ConvertStringToInt(string str)
    {
        int convertedValue = int.Parse(str);

        //(int.TryParse(str, out convertedValue))
        return convertedValue;
    }

The code is working fine except one thing.

I created Unit Test for the above method, the TestMethod is below

        /// <summary>
        ///A test for ConvertListOfStringToListOfInt
        ///</summary>
        [TestMethod()]
        public void ConvertListOfStringToListOfIntTest()
        {
            List<string> listOfStr = new List<string> { "1", "2", "3"}; // TODO: Initialize to an appropriate value
            List<int> expected = new List<int> { 1, 2, 3}; // TODO: Initialize to an appropriate value
            List<int> actual;
            actual = Conversions.ConvertListOfStringToListOfInt(listOfStr);
            Assert.AreEqual(expected, actual);
            //Assert.Inconclusive("Verify the correctness of this test method.");
        }

I have given the same values into the list I pass the method and expected list, just different by type(expected is a list of integer and passed list is a list of strings). I run the test and got this Error Message:

Assert.AreEqual failed. Expected:<System.Collections.Generic.List`1[System.Int32]>. Actual:<System.Collections.Generic.List`1[System.Int32]>.

Well, the types are actually equal so I thought there might be something different inside the lists and I debugged it.

It turned out listOfStr.Capacity is 4 and has null item as the [3] item in it’s items member, for same place in items member expected has a 0 and expected.Capacity is 4,too.

However, actual.Capacity is 3 and it actually does have 3 items in it’s items member.

I tried to newing actual before filling it and using list.Add() for adding values to expected and newing list in the ConvertListOfStringToListOfInt method. But the capacities are still the same. I do not want to set the capacity manually because this method will not be used for lists which has determined capaties.

What can I do to pass this test?
Why is the capacities different?
And how is the capacity of lists are determined, what do they depend on?

This is .NET Framework 4.0.

Answer 1

Try this:

Assert.IsTrue(actual.SequenceEqual(expected));

The reason being is that lists are complex objects and equality for lists is not determined by each element being the same, rather it is defined as are they pointing to the same list. The sequence equal method iterates the lists for you and determines equality at the item level.

If the items of the list were complex types, then it would use the default equality comparer for those items.