Test HTTP via httptest.NewServer, not gock/httpmock

byob-http-client.4 concurrencyhttptesting

Problem: HTTP mocking libraries (gock, httpmock) monkey-patch the default transport or install package-level interceptors. That fights byob-testing.1 (inject test doubles through the Factory, never monkey-patch globals) and hides real behavior — connection reuse, header handling, content-length mismatches — behind a mock layer that doesn't match production.

Idea: tests construct a real server with httptest.NewServer, point the client at its .URL, and write a http.Handler that returns the canned responses. The Factory's HTTPClient closure is overridden with one whose base URL is the test server. This mirrors byob-storage.6 (real sqlite backend in tests) — same discipline, same payoff: the test exercises the production code path.

Tradeoffs: slightly more code per test than gock's Mock().Get().Reply(). In exchange, tests catch real issues (response-body-not-closed, incorrect Content-Type parsing, retry behavior under server 503) that a mock library abstracts away. Real network loopback on localhost is fast enough that parallel tests don't care.

Design

func TestListItems(t *testing.T) {
    srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        if r.URL.Path != "/items" {
            http.Error(w, "not found", http.StatusNotFound); return
        }
        w.Header().Set("Content-Type", "application/json")
        fmt.Fprintln(w, `{"items":[{"id":1,"name":"a"}]}`)
    }))
    t.Cleanup(srv.Close)

    f := testFactory(t, srv.URL) // Factory whose HTTPClient points at srv.URL
    items, err := listItems(t.Context(), f)
    // ... assertions
}

For flaky-network simulations (retry tests), respond 503 with a Retry-After on the first attempt and 200 on the second, counting requests with an atomic.