Stub hasRosetta for tests

pkg/cmd/extension/manager.go

@@ -771,7 +771,7 @@ func possibleDists() []string {
 	}
 }
 
-func hasRosetta() bool {
+var hasRosetta = func() bool {
 	_, err := os.Stat("/Library/Apple/usr/libexec/oah/libRosettaRuntime")
 	return err == nil
 }

pkg/cmd/extension/manager_test.go

@@ -912,6 +912,58 @@ func TestManager_Install_binary_unsupported(t *testing.T) {
 	assert.Equal(t, "", stderr.String())
 }
 
+func TestManager_Install_rosetta_fallback_not_found(t *testing.T) {
+	repo := ghrepo.NewWithHost("owner", "gh-bin-ext", "example.com")
+
+	reg := httpmock.Registry{}
+	defer reg.Verify(t)
+	client := http.Client{Transport: &reg}
+
+	reg.Register(
+		httpmock.REST("GET", "api/v3/repos/owner/gh-bin-ext/releases/latest"),
+		httpmock.JSONResponse(
+			release{
+				Assets: []releaseAsset{
+					{
+						Name:   "gh-bin-ext-darwin-amd64",
+						APIURL: "https://example.com/release/cool",
+					},
+				},
+			}))
+	reg.Register(
+		httpmock.REST("GET", "api/v3/repos/owner/gh-bin-ext/releases/latest"),
+		httpmock.JSONResponse(
+			release{
+				Tag: "v1.0.1",
+				Assets: []releaseAsset{
+					{
+						Name:   "gh-bin-ext-darwin-amd64",
+						APIURL: "https://example.com/release/cool",
+					},
+				},
+			}))
+
+	ios, _, stdout, stderr := iostreams.Test()
+	tempDir := t.TempDir()
+
+	m := newTestManager(tempDir, &client, nil, ios)
+	m.platform = func() (string, string) {
+		return "darwin-arm64", ""
+	}
+
+	originalHasRosetta := hasRosetta
+	t.Cleanup(func() { hasRosetta = originalHasRosetta })
+	hasRosetta = func() bool {
+		return false
+	}
+
+	err := m.Install(repo, "")
+	assert.EqualError(t, err, "gh-bin-ext unsupported for darwin-arm64. Install Rosetta with `softwareupdate --install-rosetta` to use the available darwin-amd64 binary, or open an issue: `gh issue create -R owner/gh-bin-ext -t'Support darwin-arm64'`")
+
+	assert.Equal(t, "", stdout.String())
+	assert.Equal(t, "", stderr.String())
+}
+
 func TestManager_Install_binary(t *testing.T) {
 	repo := ghrepo.NewWithHost("owner", "gh-bin-ext", "example.com")