First Expectation cannot be overwritten

[tgsmith61591]

Explanation

Once .expect_foo() is called on a mock instance, the return value cannot be overwritten.

Consider the following example:

    #[mockall::automock]
    trait Kek {
        fn kek(&self) -> u8;
    }
    #[test]
    fn test_kek() {
        let mut kek = MockKek::new();
        kek.expect_kek().returning(|| 1);
        kek.expect_kek().returning(|| 2);

        let got = kek.kek();
        assert_eq!(got, 2, "want 2, got: {}", got); // Oh no, got 1!!!!
    }

So what? Why not just call it once?

Well, imagine a trait that has many methods, and creation of a default mock is placed into a testing fixture, and each test is responsible for setting up its expected return value. Perhaps something like:

#[rstest::fixture]
fn mock_kek() -> MockKek {
        let mut kek = MockKek::new();
        kek.expect_kek().returning(|| u8::default());
        kek.expect_foo().returning(|| u8::default());
        kek.expect_bar().returning(|| u8::default());
        // ...
        kek.expect_qux().returning(|| u8::default());
        kek
}

#[rstest]
fn test_kek(mut mock_kek: MockKek) {
        kek.expect_kek().returning(|| 2);
        let got = kek.kek();
        assert_eq!(got, 2, "want 2, got: {}", got); // Oh no, we get u8::default()!
}

Expected behavior

I would expect that calling .expect_kek() again would allow me to overwrite the default setup in the fixture.
Is there a clear way around this, or is this a case of me just misusing the tool?

[asomers]

What you're doing is creating two expectations. The second will only be used once the first is satisfied. But since you didn't specify any .times() limit, the first will never be satisfied. There is no facility for overriding an existing expectation.