I know it's meant to simulate the actual transport middlewares, but it seems like a trivial assertion, when we set the UA header in the outer transport and then we capture it in the inner one.

In other words, the test should only assert the auth header is set.

I think the point with the user-agent assertion is to ensure the header isn't being mutated. I know it's a trivial assertion, but I guess tests are cheap. If we really care that this user agent isn't mutated in between somehow, it seems like a fair idea.

BTW, (nit) I would prefer if this test code was a bit more readable by breaking apart this code.

	// Inner transport captures headers as-received to verify they survived the wrapping.
	innerTransport := &roundTripper{
		roundTrip: func(req *http.Request) (*http.Response, error) {
			receivedUA = req.Header.Get("User-Agent")
			receivedAuth = req.Header.Get("Authorization")
			return &http.Response{
				StatusCode: 200,
				Header:     http.Header{"Content-Type": []string{"application/json"}},
				Body:       io.NopCloser(bytes.NewBufferString(`{"data":{"viewer":{"login":"monalisa"}}}`)),
				Request:    req,
			}, nil
		},
	}

	// Outer transport sets User-Agent, simulating the factory-built client's header middleware.
	plainClient := &http.Client{
		Transport: &roundTripper{
			roundTrip: func(req *http.Request) (*http.Response, error) {
				req.Header.Set("User-Agent", "GitHub CLI 1.2.3 Agent/copilot-cli")
				return innerTransport.RoundTrip(req)
			},
		},
	}

Yeah, I thought about that, too. But it can't be the case either. Because the new transport that getViewer makes, will wrap the HTTP client's transport (the two-layer we build in the test). I mean, there's no way for getViewer to add a transport in the middle of the chain.

We don't need the two layers. Only one is enough. However, we can check the UA header is not set, as an assertion that getViewer has nothing to do wth it (and therefore further transport layers see the UA header is unset, and would then safely add it).