Go Testing Strategy for http.NewRequest to an endpoint with "Connection" "keep-alive" header

I'm currently trying to brainstorm and scope some possible ways to test a request to an endpoint that returns a SSE stream.

This, in part, shows my existing test-stagey for any requests that I'd like to make:

for _, test := range tests {
        req, _ := http.NewRequest(
            "GET",
            test.route,
            nil,
        )

        // Perform the request plain with the app.
        // The -1 disables request latency.
        res, err := r.Test(req, -1)

        // verify that no error occured, that is not expected
        assert.Equalf(t, test.expectedError, err != nil, test.description)

        // As expected errors lead to broken responses, the next
        // test case needs to be processed
        if test.expectedError {
            continue
        }

        // Verify if the status code is as expected
        assert.Equalf(t, test.expectedCode, res.StatusCode, test.description)

        // Read the response body
        body, err := ioutil.ReadAll(res.Body)

        defer res.Body.Close()

        // Reading the response body should work everytime, such that
        // the err variable should be nil
        assert.Nilf(t, err, test.description)

        // Verify, that the reponse body equals the expected body
        if len(test.expectedBody) > 0 {
            assert.Equalf(t, string(test.expectedBody), string(body), test.description)
        }
    }

However, when I add a route to my test runner that is to a connection that doesn't automatically close and instead is kept alive, my tests, obviously, will never finish.

Is there a way / pattern to test such keep-alive endpoints? I just really want to get the first sent event, and then close the connection.

I have tried A LOT, but nothing seems to close the damn connection programatically.

Any pro-tips on how to achieve this, would be excellent!