• Getting started
• Creating a substitute
• Setting a return value
• Return for specific args
• Return for any args
• Return from a function
• Multiple return values
• Replacing return values
• Checking received calls
• Clearing received calls
• Argument matchers
• Callbacks, void calls and When..Do
• Throwing exceptions
• Raising events
• Auto and recursive mocks
• Setting out and ref args
• Actions with argument matchers
• Checking call order
• Partial subs and test spies
• Return for all calls of a type
• Threading

Setting out and ref args

Out and ref arguments can be set using a Returns() callback, or using When..Do.

public interface ILookup {
    bool TryLookup(string key, out string value);
}

For the interface above we can configure the return value and set the output of the second argument like this:

//Arrange
var value = "";
var lookup = Substitute.For<ILookup>();
lookup
    .TryLookup("hello", out value)
    .Returns(x => { 
        x[1] = "world!";
        return true;
    });

//Act
var result = lookup.TryLookup("hello", out value);

//Assert
Assert.True(result);
Assert.AreEqual(value, "world!");