AssignableFrom Constraint

AssignableFromConstraint tests that an instance of the specified type can be assigned to the actual value's type. In other words, the actual value's type is a base type or interface of the expected type.

Usage

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

Examples

[Test]
public void AssignableFromConstraint_Examples()
{
    // A string variable can be assigned from string
    Assert.That("Hello", Is.AssignableFrom(typeof(string)));
    Assert.That("Hello", Is.AssignableFrom<string>());

    // An object variable can be assigned from string (string derives from object)
    Assert.That(new object(), Is.AssignableFrom<string>());

    // An IEnumerable variable can be assigned from List<int>
    IEnumerable<int> items = new List<int>();
    Assert.That(items, Is.AssignableFrom<List<int>>());

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

Notes

  1. Is.AssignableFrom<T>() is true when actualType.IsAssignableFrom(typeof(T)).
  2. This tests "can I assign an instance of T to this variable?".
  3. This is the reverse of AssignableToConstraint.

See Also