A call can be configured to return a value regardless of the arguments passed using the ReturnsForAnyArgs() extension method.

calculator.Add(1, 2).ReturnsForAnyArgs(100);
Assert.That(calculator.Add(1, 2), Is.EqualTo(100));
Assert.That(calculator.Add(-7, 15), Is.EqualTo(100));

Tip! You can also use the default C# keyword for better readability:

calculator.Add(default, default).ReturnsForAnyArgs(100);

The same behaviour can also be achieved using argument matchers: it is simply a shortcut for replacing each argument with Arg.Any<T>().

ReturnsForAnyArgs() has the same overloads as Returns(), so you can also specify multiple return values or calculated return values using this approach.