198 words (approximately 1 min)

Overview [ Documentation]

Argument matchers provide a way to:

  1. specify a call or group of calls so that a return value can be set for all matching calls
  2. check a matching call has been received

Argument matchers can be used:

  1. when setting return values (with a call to Returns())
  2. when validating calls (with a call to Received())

Uses

Ignoring Arguments

Use Arg.Any<T>() to ignore an argument of type T:

calculator.Add(Arg.Any<int>(), 5).Returns(7);

Assert.AreEqual(7, calculator.Add(42, 5));
Assert.AreEqual(7, calculator.Add(123, 5)); 
Assert.AreNotEqual(7, calculator.Add(1, 7));

Match an Argument

Use Arg.Is<T>(T value) to match an argument of type T:

calculator.Add(0, 42);
calculator.Received().Add(Arg.Is(0), Arg.Any<int>());

Conditionally Match an Argument

Use Arg.Is<T>(Predicate<T> condition) to conditionally match an argument of type T:

calculator.Add(1, -10);

// Received call with first arg 1 and second arg less than 0:
calculator.Received().Add(1, Arg.Is<int>(x => x < 0));

// Received call with first arg 1 and second arg of -2, -5, or -10:
calculator.Received().Add(1, Arg.Is<int>(x => new[] {-2,-5,-10}.Contains(x)));

// Did not receive call with first arg greater than 10:
calculator.DidNotReceive().Add(Arg.Is<int>(x => x > 10), -10);

Match out and ref Arguments

calculator.LoadMemory(1, out Arg.Any<int>())
          .Returns(x => 
          {
              x[1] = 42;
              return true;
          });

var hasEntry = calculator.LoadMemory(1, out var memoryValue);

Assert.AreEqual(true, hasEntry);
Assert.AreEqual(42, memoryValue);