diff --git a/pkg/cmd/pr/update/update_test.go b/pkg/cmd/pr/update/update_test.go
new file mode 100644
index 000000000..be6e192b6
--- /dev/null
+++ b/pkg/cmd/pr/update/update_test.go
@@ -0,0 +1,229 @@
+package update
+
+import (
+	"bytes"
+	"net/http"
+	"testing"
+
+	"github.com/cli/cli/v2/api"
+	"github.com/cli/cli/v2/git"
+	"github.com/cli/cli/v2/internal/ghrepo"
+	shared "github.com/cli/cli/v2/pkg/cmd/pr/shared"
+	"github.com/cli/cli/v2/pkg/cmdutil"
+	"github.com/cli/cli/v2/pkg/httpmock"
+	"github.com/cli/cli/v2/pkg/iostreams"
+	"github.com/google/shlex"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNewCmdUpdate(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		output   UpdateOptions
+		wantsErr string
+	}{
+		{
+			name:   "no argument",
+			input:  "",
+			output: UpdateOptions{},
+		},
+		{
+			name:  "with argument",
+			input: "23",
+			output: UpdateOptions{
+				SelectorArg: "23",
+			},
+		},
+		{
+			name:  "no argument, --rebase",
+			input: "--rebase",
+			output: UpdateOptions{
+				Rebase: true,
+			},
+		},
+		{
+			name:  "with argument, --rebase",
+			input: "23 --rebase",
+			output: UpdateOptions{
+				SelectorArg: "23",
+				Rebase:      true,
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ios, _, _, _ := iostreams.Test()
+			ios.SetStdoutTTY(true)
+			ios.SetStdinTTY(true)
+			ios.SetStderrTTY(true)
+
+			f := &cmdutil.Factory{
+				IOStreams: ios,
+			}
+
+			argv, err := shlex.Split(tt.input)
+			assert.NoError(t, err)
+
+			var gotOpts *UpdateOptions
+			cmd := NewCmdUpdate(f, func(opts *UpdateOptions) error {
+				gotOpts = opts
+				return nil
+			})
+
+			cmd.SetArgs(argv)
+			cmd.SetIn(&bytes.Buffer{})
+			cmd.SetOut(&bytes.Buffer{})
+			cmd.SetErr(&bytes.Buffer{})
+
+			_, err = cmd.ExecuteC()
+			if tt.wantsErr != "" {
+				assert.EqualError(t, err, tt.wantsErr)
+				return
+			}
+
+			assert.NoError(t, err)
+			assert.Equal(t, tt.output.SelectorArg, gotOpts.SelectorArg)
+			assert.Equal(t, tt.output.Rebase, gotOpts.Rebase)
+		})
+	}
+}
+
+func Test_updateRun(t *testing.T) {
+	defaultInput := func() UpdateOptions {
+		return UpdateOptions{
+			Finder: shared.NewMockFinder("123", &api.PullRequest{
+				ID:         "123",
+				HeadRefOid: "head-ref-oid",
+			}, ghrepo.New("OWNER", "REPO")),
+		}
+	}
+
+	tests := []struct {
+		name      string
+		input     *UpdateOptions
+		httpStubs func(*testing.T, *httpmock.Registry)
+		stdout    string
+		stderr    string
+		wantsErr  string
+	}{
+		{
+			name: "success, merge",
+			input: &UpdateOptions{
+				SelectorArg: "123",
+			},
+			httpStubs: func(t *testing.T, reg *httpmock.Registry) {
+				reg.Register(
+					httpmock.GraphQL(`mutation PullRequestUpdateBranch\b`),
+					httpmock.GraphQLMutation(`{
+						"data": {
+							"updatePullRequestBranch": {
+								"pullRequest": {}
+							}
+						}
+					}`, func(inputs map[string]interface{}) {
+						assert.Equal(t, "123", inputs["pullRequestId"])
+						assert.Equal(t, "head-ref-oid", inputs["expectedHeadOid"])
+						assert.Equal(t, "MERGE", inputs["updateMethod"])
+					}))
+			},
+			stdout: "",
+			stderr: "✓ PR branch updated\n",
+		},
+		{
+			name: "success, rebase",
+			input: &UpdateOptions{
+				SelectorArg: "123",
+				Rebase:      true,
+			},
+			httpStubs: func(t *testing.T, reg *httpmock.Registry) {
+				reg.Register(
+					httpmock.GraphQL(`mutation PullRequestUpdateBranch\b`),
+					httpmock.GraphQLMutation(`{
+						"data": {
+							"updatePullRequestBranch": {
+								"pullRequest": {}
+							}
+						}
+					}`, func(inputs map[string]interface{}) {
+						assert.Equal(t, "123", inputs["pullRequestId"])
+						assert.Equal(t, "head-ref-oid", inputs["expectedHeadOid"])
+						assert.Equal(t, "REBASE", inputs["updateMethod"])
+					}))
+			},
+			stdout: "",
+			stderr: "✓ PR branch updated\n",
+		},
+		{
+			name: "failure, pr not found",
+			input: &UpdateOptions{
+				Finder:      shared.NewMockFinder("", nil, nil),
+				SelectorArg: "123",
+			},
+			wantsErr: "no pull requests found",
+		},
+		{
+			name: "failure, API error",
+			input: &UpdateOptions{
+				SelectorArg: "123",
+			},
+			httpStubs: func(t *testing.T, reg *httpmock.Registry) {
+				reg.Register(
+					httpmock.GraphQL(`mutation PullRequestUpdateBranch\b`),
+					httpmock.GraphQLMutation(`{
+						"data": {},
+						"errors": [
+							{
+								"message": "some error"
+							}
+						]
+					}`, func(inputs map[string]interface{}) {
+						assert.Equal(t, "123", inputs["pullRequestId"])
+						assert.Equal(t, "head-ref-oid", inputs["expectedHeadOid"])
+						assert.Equal(t, "MERGE", inputs["updateMethod"])
+					}))
+			},
+			wantsErr: "GraphQL: some error",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ios, _, stdout, stderr := iostreams.Test()
+			ios.SetStdoutTTY(true)
+			ios.SetStdinTTY(true)
+			ios.SetStderrTTY(true)
+
+			reg := &httpmock.Registry{}
+			defer reg.Verify(t)
+			if tt.httpStubs != nil {
+				tt.httpStubs(t, reg)
+			}
+
+			tt.input.GitClient = &git.Client{
+				GhPath:  "some/path/gh",
+				GitPath: "some/path/git",
+			}
+
+			if tt.input.Finder == nil {
+				tt.input.Finder = defaultInput().Finder
+			}
+
+			httpClient := func() (*http.Client, error) { return &http.Client{Transport: reg}, nil }
+
+			tt.input.IO = ios
+			tt.input.HttpClient = httpClient
+
+			err := updateRun(tt.input)
+
+			if tt.wantsErr != "" {
+				assert.EqualError(t, err, tt.wantsErr)
+				return
+			} else {
+				assert.NoError(t, err)
+			}
+
+			assert.Equal(t, tt.stdout, stdout.String())
+			assert.Equal(t, tt.stderr, stderr.String())
+		})
+	}
+}