Why does this test involving Swap.NextInstance() fail?

Hi Neil,

When using Swap.NextInstance() the aim is to replace behavior unreachable in the test (because it's on an object instantiated in the code under test), with behavior defined on a fake object. Because the swapped instance is normally unreachable, verifying against it is unsupported. Instead, you should verify against the fake you substitute it with:

var fake = Isolate.Fake.Instance<A>();
Isolate.Swap.NextInstance<A>().With(fake);

// this is the future instance, it is normally not instantiated in the test context
A a = new A();
a.AMethod();

// in the test context we verify against the fake we created earlier in the test
Isolate.Verify.WasCalledWithExactArguments(() => fake.AMethod());

Please let me know if this helps.

Doron
Typemock Support

Hi Doron,

That code helps and works, thanks.