Mocking HTTP calls for Unit tests in Rust

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Motivation: HTTP calls should be mocked, we don’t want to make HTTP calls every time we run our tests and it also makes them faster to run!

The tutorial will be referring to httpmock v0.4.2 mocking library (There are other mocking libraries like mockito

Where to begin?

Let’s start with how you can import httpmock

[dev-dependencies]
httpmock = "0.4.2"

Now, let’s mock something with this amazing library

// you could import any of the HTTP methods you are using
use httpmock::Method::GET;
use httpmock::{Mock, MockServer};
...

fn test_with_mock_server() {
    
    let mock_server = MockServer::start();
    
    // you can also connect to a remote server using connect()
    let server = MockServer::connect("server_address");
    // create a mock on mock_server
    let mock = Mock::new()
        .expect_method(GET)
        .expect_path("/hello")
        .return_status(200)
        .create_on(&mock_server);
    // we can find out number of times mock is invoked
    assert_eq!(hello_mock.times_called(), 1);
    // mocks can also be deleted
    hello_mock.delete();
}

And that is it, you can now mock HTTP requests in Rust

If you need to inject your mock_server’s URL into a struct, you can use mock_server.url(“”) to fetch the mock_server’s address in case you used the MockServer::start() method.