Fluent API allows setting up a second callback that won't get involved if .Throws() is specified too

[stakx]

This is currently (as of version 4.9.0) possible:

bool (firstCallbackInvoked, secondCallbackInvoked) = (false, false);

var mock = new Mock<object>();
mock.Setup(m => m.ToString())
    .Callback(() => firstCallbackInvoked = true)
    .Returns(() => default(string))
    .Callback(() => secondCallbackInvoked = true)
    .Throws<Exception>();

Assert.Throws<Exception>(() => mock.Object.ToString());
Assert.True(firstCallbackInvoked);
Assert.True(secondCallbackInvoked);

This fails because the second callback never gets invoked.

(This test doesn't make sense because it returns and throws simultaneously; see #665 concerning that. If the pattern of returning-then-throwing is forbidden, then we won't have to fix anything here.)

[stakx]

This will be tracked in #668 along with some other closely related issues.