Remove network requests from actions.NewClient (#2219)

Co-authored-by: Nikola Jokic <jokicnikola07@gmail.com>

github/actions/byte_order_mark_test.go

@@ -0,0 +1,61 @@
+package actions_test
+
+import (
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/actions/actions-runner-controller/github/actions"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestClient_Do(t *testing.T) {
+	t.Run("trims byte order mark from response if present", func(t *testing.T) {
+		t.Run("when there is no body", func(t *testing.T) {
+			server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			}))
+			defer server.Close()
+
+			client, err := actions.NewClient("https://localhost/org/repo", &actions.ActionsAuth{Token: "token"})
+			require.NoError(t, err)
+
+			req, err := http.NewRequest("GET", server.URL, nil)
+			require.NoError(t, err)
+
+			resp, err := client.Do(req)
+			require.NoError(t, err)
+
+			body, err := io.ReadAll(resp.Body)
+			require.NoError(t, err)
+			assert.Empty(t, string(body))
+		})
+
+		responses := []string{
+			"\xef\xbb\xbf{\"foo\":\"bar\"}",
+			"{\"foo\":\"bar\"}",
+		}
+
+		for _, response := range responses {
+			server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				w.Header().Set("Content-Type", "application/json")
+				w.Write([]byte(response))
+			}))
+			defer server.Close()
+
+			client, err := actions.NewClient("https://localhost/org/repo", &actions.ActionsAuth{Token: "token"})
+			require.NoError(t, err)
+
+			req, err := http.NewRequest("GET", server.URL, nil)
+			require.NoError(t, err)
+
+			resp, err := client.Do(req)
+			require.NoError(t, err)
+
+			body, err := io.ReadAll(resp.Body)
+			require.NoError(t, err)
+			assert.Equal(t, "{\"foo\":\"bar\"}", string(body))
+		}
+	})
+}