Getting "Do not return promises from tests declared via test.cb" error

[gajus]

$ ava --version
0.14.0

I am getting an error:

✖ createHttpProxyServer › proxies HTTP POST request failed with "Do not return promises from tests declared via test.cb(...), > if you want to return a promise simply declare the test via test(...)"
Unhandled Rejection: tests/createHttpProxyServer.js
TypeError: proxyServer is not a function
resolve (/Users/gajus/Documents/dev/applaudience/forward-proxy/src/createHttpProxyServer.js:72:9)
exports.default.options (/Users/gajus/Documents/dev/applaudience/forward-proxy/src/createHttpProxyServer.js:56:12)
Test. (createHttpProxyServer.js:67:5)
Test._ava2.default.cb as fn

I understand what the error is telling me. I don't understand what is this limitation for?

Consider this test:

test.cb('proxies HTTP POST request', async (t) => {
    t.plan(1);

    const handleRequest = async (requestDefinition) => {
        t.deepEqual(requestDefinition, {
            headers: {
                'content-length': '13',
                connection: 'close',
                host: 'gajus.com'
            },
            method: 'post',
            payload: 'Hello, World!',
            url: 'http://gajus.com/'
        });

        return createHttpResponse();
    };

    const resolvedServer = await createHttpProxyServer({
        handleRequest,
        port: 8000
    });

    await request('http://gajus.com', {
        ...defaultRequestOptions,
        method: 'post',
        body: 'Hello, World!'
    });

    resolvedServer.destroy();

    t.end();
});

As it is, ava cannot execute this test. I need to rewrite it to:

test.cb('proxies HTTP POST request', (t) => {
    t.plan(1);

    const handleRequest = async (requestDefinition) => {
        t.deepEqual(requestDefinition, {
            headers: {
                'content-length': '13',
                connection: 'close',
                host: 'gajus.com'
            },
            method: 'post',
            payload: 'Hello, World!',
            url: 'http://gajus.com/'
        });

        return createHttpResponse();
    };

    createHttpProxyServer({
        handleRequest,
        port: 8000
    })
        .then((resolvedServer) => {
            console.log('Hello!');

            return request('http://gajus.com', {
                ...defaultRequestOptions,
                method: 'post',
                body: 'Hello, World!'
            })
                .then(() => {
                    resolvedServer.destroy();

                    t.end();
                });
        });
});

What is the reason for the limitation?

[jamestalmage]

You are using t.end incorrectly. Don't use it as a timeout method (don't use it at all here). Avoid test.cb when returning promises.

The reason is because AVA needs to know when to end the test. You can defer ending a test by returning a promise, or using test.cb / t.end. We don't allow both because that makes the end of the test ambiguous.