## List Mapper (NUnit 2.4.2)

Unlike Constraint classes, ListMapper is used to modify the actual value argument to Assert.That(). It transforms the actual value, which must be a collection, creating a new collection to be tested against the supplied constraint. Currently, ListMapper supports one transformation: creating a collection of property values.

Normally, ListMapper will be used through the List.Map() syntax helper or the inherited syntax equivalent, Map(). The following example shows three forms of the same assert:

    string[] strings = new string[] { "a", "ab", "abc" };
    int[] lengths = new int[] { 1, 2, 3 };

    Assert.That(List.Map(strings).Property("Length"),
           Is.EqualTo(lengths));

    Assert.That(new ListMapper(strings).Property("Length"),
           Is.EqualTo(lengths));

    // Assuming inheritance from AssertionHelper
    Expect(Map(strings).Property("Length"), EqualTo(lengths));