Crate wiremock

wiremock provides HTTP mocking to perform black-box testing of Rust applications that interact with third-party APIs.

It provides mocking of HTTP responses using request matching and response templating.

Table of Contents

1. Getting started
2. Matchers
3. Test isolation
4. Runtime compatibility
5. Prior art
6. Future evolution

Getting started

use wiremock::{MockServer, Mock, ResponseTemplate};
use wiremock::matchers::{method, path};

#[async_std::main]
async fn main() {
    // Start a background HTTP server on a random local port
    let mock_server = MockServer::start().await;

    // Arrange the behaviour of the MockServer adding a Mock:
    // when it receives a GET request on '/hello' it will respond with a 200.
    Mock::given(method("GET"))
        .and(path("/hello"))
        .respond_with(ResponseTemplate::new(200))
        // Mounting the mock on the mock server - it's now effective!
        .mount(&mock_server)
        .await;
     
    // If we probe the MockServer using any HTTP client it behaves as expected.
    let status = surf::get(format!("{}/hello", &mock_server.uri()))
        .await
        .unwrap()
        .status();
    assert_eq!(status.as_u16(), 200);

    // If the request doesn't match any `Mock` mounted on our `MockServer` a 404 is returned.
    let status = surf::get(format!("{}/missing", &mock_server.uri()))
        .await
        .unwrap()
        .status();
    assert_eq!(status.as_u16(), 404);
}

Matchers

wiremock provides a set of matching strategies out of the box - check the matchers module for a complete list.

You can define your own matchers using the Match trait, as well as using Fn closures.
Check Match's documentation for more details and examples.

Test isolation

Each instance of MockServer is fully isolated: start takes care of finding a random port available on your local machine which is assigned to the new MockServer.

You should use one instance of MockServer for each test, to ensure full isolation and no cross-test interference.

When a MockServer instance goes out of scope (e.g. the test finishes), the corresponding HTTP server running in the background is shut down to free up the port it was using.

Runtime compatibility

wiremock can be used (and it is tested to work) with both async_std and tokio as futures runtimes.
If you encounter any compatibility bug, please open an issue on our GitHub repository.

Prior art

mockito and httpmock provide HTTP mocking for Rust.

Check the table below to see how wiremock compares to them across the following dimensions:

• Test execution strategy (do tests have to be executed sequentially or can they be executed in parallel?);
• How many APIs can I mock in a test?
• Out-of-the-box request matchers;
• Extensible request matching (i.e. you can define your own matchers);
• Sync/Async API;
• Spying (e.g. verify that a mock has/hasn't been called in a test);
• Standalone mode (i.e. can I launch an HTTP mock server outside of a test suite?).

	Test execution strategy	How many APIs can I mock?	Out-of-the-box request matchers	Extensible request maching	API	Spying	Standalone mode
mockito	❌ Sequential	❌ 1	✔	❌	Sync	✔	❌
httpmock	❌ Sequential	❌ 1	✔	❌	Sync	✔	✔
wiremock	✔ Parallel ️	✔ Unbounded	✔	✔	Async	❌	❌

Future evolution

Spying is in scope for future releases of wiremock.
More request matchers can be added to those provided out-of-the-box to handle common usecases.

Modules

matchers

A collection of different matching strategies provided out-of-the-box by wiremock.

Structs

Mock	Given a set of matchers, a Mock instructs an instance of MockServer to return a pre-determined response if the matching conditions are satisfied.
MockBuilder	A fluent builder to construct a Mock instance given matchers and a ResponseTemplate.
MockServer	An HTTP web-server running in the background to behave as one of your dependencies using Mocks for testing purposes.
Request	An incoming request to an instance of MockServer.
ResponseTemplate	The blueprint for the response returned by a MockServer when a Mock matches on an incoming request.

Traits

Match

Anything that implements Match can be used to constrain when a Mock is activated.