AssignableTo Constraint

AssignableToConstraint tests that the actual value can be assigned to a variable of the specified type. In other words, the actual value's type derives from or implements the expected type.

Usage

Is.AssignableTo(Type expectedType)
Is.AssignableTo<T>()

Examples

[Test]
public void AssignableToConstraint_Examples()
{
    // A string can be assigned to object (string derives from object)
    Assert.That("Hello", Is.AssignableTo(typeof(object)));
    Assert.That("Hello", Is.AssignableTo<object>());

    // A string can be assigned to IEnumerable<char>
    Assert.That("Hello", Is.AssignableTo<IEnumerable<char>>());

    // A List<int> can be assigned to IList<int>
    Assert.That(new List<int>(), Is.AssignableTo<IList<int>>());
    Assert.That(new List<int>(), Is.AssignableTo<IEnumerable<int>>());

    // Negative: an int cannot be assigned to string
    Assert.That(5, Is.Not.AssignableTo(typeof(string)));
}

Notes

  1. Is.AssignableTo<T>() is true when typeof(T).IsAssignableFrom(actual.GetType()).
  2. This tests "can this value be assigned to a variable of type T?".
  3. This is the reverse of AssignableFromConstraint.

See Also