Go 为超时的单元测试创​​建 deadlineExceededError：true

为了不使测试过于复杂，我建议您使用这种方法.首先，定义您的错误:

type timeoutError struct {
    err     string
    timeout bool
}

func (e *timeoutError) Error() string {
    return e.err
}

func (e *timeoutError) Timeout() bool {
    return e.timeout
}

In this way, timeoutError implements both the Error() and Timeout interfaces.
Then you've to define the mock for the HTTP client:

type mockClient struct{}

func (m *mockClient) Do(req *http.Request) (*http.Response, error) {
    return nil, &timeoutError{
        err:     "context deadline exceeded (Client.Timeout exceeded while awaiting headers)",
        timeout: true,
    }
}

这只是返回上面定义的错误，并将nil作为HTTP.Response返回.最后，让我们看看如何编写一个样例单元测试:

func TestSlowServer(t *testing.T) {
    r := httptest.NewRequest(http.MethodGet, "http://example.com", nil)
    client := &mockClient{}

    _, err := client.Do(r)

    fmt.Println(err.Error())
}

If you debug this test and pause with the debugger on the err variable, you'll see the wanted result.
Thanks to this approach you can achieve what you need without bringing in any extra complexity. Let me know if works for you!