client: tidy-up mock-utilities

- Add a `mockResponse` utility, and slightly enhance it to also include
  the request Headers and Status message, to be more closely to actual
  responses.
- Add a `mockJSONResponse` utility, implemented using `mockResponse`
- Remove `plainTextErrorMock` in favor of `mockResponse`

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

client/client_mock_test.go

@@ -1,7 +1,6 @@
 package client
 
 import (
-	"bytes"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -50,30 +49,41 @@ func WithMockClient(doer func(*http.Request) (*http.Response, error)) Opt {
 }
 
 func errorMock(statusCode int, message string) func(req *http.Request) (*http.Response, error) {
+	return mockJSONResponse(statusCode, nil, common.ErrorResponse{
+		Message: message,
+	})
+}
+
+func mockJSONResponse[T any](statusCode int, headers http.Header, resp T) func(req *http.Request) (*http.Response, error) {
+	respBody, err := json.Marshal(&resp)
+	if err != nil {
+		panic(err)
+	}
+	hdr := make(http.Header)
+	if headers != nil {
+		hdr = headers.Clone()
+	}
+	hdr.Set("Content-Type", "application/json")
+	return mockResponse(statusCode, hdr, string(respBody))
+}
+
+func mockResponse(statusCode int, headers http.Header, respBody string) func(req *http.Request) (*http.Response, error) {
+	if headers == nil {
+		headers = make(http.Header)
+	}
+	var body io.ReadCloser
+	if respBody == "" {
+		body = http.NoBody
+	} else {
+		body = io.NopCloser(strings.NewReader(respBody))
+	}
 	return func(req *http.Request) (*http.Response, error) {
-		header := http.Header{}
-		header.Set("Content-Type", "application/json")
-
-		body, err := json.Marshal(&common.ErrorResponse{
-			Message: message,
-		})
-		if err != nil {
-			return nil, err
-		}
-
 		return &http.Response{
+			Status:     fmt.Sprintf("%d %s", statusCode, http.StatusText(statusCode)),
 			StatusCode: statusCode,
-			Body:       io.NopCloser(bytes.NewReader(body)),
-			Header:     header,
-		}, nil
-	}
-}
-
-func plainTextErrorMock(statusCode int, message string) func(req *http.Request) (*http.Response, error) {
-	return func(req *http.Request) (*http.Response, error) {
-		return &http.Response{
-			StatusCode: statusCode,
-			Body:       io.NopCloser(bytes.NewReader([]byte(message))),
+			Header:     headers,
+			Body:       body,
+			Request:    req,
 		}, nil
 	}
 }