public void AddEqualValidationPredicate_WhenArgumentIsDouble()
{
// Arrange.
ValidatableArgument<double> argument = new ValidatableArgument<double>("argument", 3);
// Act.
argument.IsEqual(5);
// Assert.
Assert.AreEqual(1, argument.ValidationPredicates.Count());
Assert.IsInstanceOfType(argument.ValidationPredicates.First(), typeof(EqualValidationPredicate<double>));
}