Mock Builder

"Mock builder" refers to a closure with When and Then parameters used to build the request match conditions and response, respectively.

    // A mock that returns the text "yo!" to any request
    let mock = Mock::new(|when, then| {
        when.any(); // builds a set of request match conditions
        then.text("yo!"); // builds the response to return when conditions are matched
    })

Together, they build a Mock, which consists of a set of request match conditions, a response, and a priority:

pub struct Mock {
    /// Mock ID.
    pub id: Uuid,
    /// A set of request match conditions.
    pub matchers: Vec<Arc<dyn Matcher>>,
    /// A mock response.
    pub response: Response,
    /// Priority.
    pub priority: u8, // defaults to 5 (more on this later)
    /// Match counter.
    pub match_count: AtomicUsize,
    /// Limit on how many times this mock can be matched.
    pub limit: Option<usize>,
}

Since when and then are just variables of types When and Then, you can name them however you'd like, e.g. the following also works.

    // A mock that returns the text "index" to get requests on the / endpoint
    let mock = Mock::new(|req, res| {
        req.get().path("/");
        res.text("index");
    })

We experimented with several different APIs and found this closure-builder pattern to feel the most ergonomic and nice to use.

The mock builder closure is exposed via 3 methods, allowing flexible usage patterns:

1. Mock::new(|when, then|...) to build a standalone mock
2. MockSet::mock(|when, then|...) shorthand to build a mock and insert it into the mock set
3. MockServer::mock(|when, then|...) shorthand to build a mock and insert it into the server's mock set