Go HTTP エンドポイント テストで Request.FormFile を設定する方法?

<code class="go">import (
    "bytes"
    "io"
    "io/ioutil"
    "mime/multipart"

    "net/http"
    "net/http/httptest"
    "testing"
)

func testEndpoint(t *testing.T) {
    // Create a multipart form data writer
    body := &bytes.Buffer{}
    writer := multipart.NewWriter(body)

    // Create a form file part
    part, err := writer.CreateFormFile("y", "someimg.png")
    if err != nil {
        t.Fatalf("error creating FormFile: %v", err)
    }

    // Copy a test image into the form file part
    img, err := ioutil.ReadFile("testdata/someimg.png")
    if err != nil {
        t.Fatalf("error reading image: %v", err)
    }
    if _, err = io.Copy(part, bytes.NewReader(img)); err != nil {
        t.Fatalf("error copying image: %v", err)
    }

    // Close the form data writer
    err = writer.Close()
    if err != nil {
        t.Fatalf("error closing form data writer: %v", err)
    }

    // Create a new HTTP request
    request := httptest.NewRequest("POST", "/", body)
    request.Header.Add("Content-Type", writer.FormDataContentType())

    // Test the endpoint
    // ...
}</code>