internal/telemetry/cmd/stacks: divert GitHub changes during testing

When testing, the GitHub client saves changes instead of applying
them. This makes it possible to test functions that would otherwise
alter GitHub.

Add a test for one such function, updateIssues.

Change-Id: I77a716dac346ab591ff1f94cd38e414d0082d513
Reviewed-on: https://go-review.googlesource.com/c/tools/+/643937
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Alan Donovan <[email protected]>

Author: jba

gopls/internal/telemetry/cmd/stacks/stacks.go

@@ -811,8 +811,24 @@ func frameURL(pclntab map[string]FileLine, info Info, frame string) string {
 // -- GitHub client --
 
 // A githubClient interacts with GitHub.
+// During testing, updates to GitHub are saved in changes instead of being applied.
+// Reads from GitHub occur normally.
 type githubClient struct {
-	authToken string // mandatory GitHub authentication token (for R/W issues access)
+	authToken     string // mandatory GitHub authentication token (for R/W issues access)
+	divertChanges bool   // divert attempted GitHub changes to the changes field instead of executing them
+	changes       []any  // slice of (addIssueComment | updateIssueBody)
+}
+
+// addIssueComment is a change for creating a comment on an issue.
+type addIssueComment struct {
+	number  int
+	comment string
+}
+
+// updateIssueBody is a change for modifying an existing issue's body.
+type updateIssueBody struct {
+	number int
+	body   string
 }
 
 // -- GitHub search --
@@ -874,6 +890,11 @@ func (cli *githubClient) searchIssues(label string) ([]*Issue, error) {
 
 // updateIssueBody updates the body of the numbered issue.
 func (cli *githubClient) updateIssueBody(number int, body string) error {
+	if cli.divertChanges {
+		cli.changes = append(cli.changes, updateIssueBody{number, body})
+		return nil
+	}
+
 	// https://docs.github.com/en/rest/issues/comments#update-an-issue
 	var payload struct {
 		Body string `json:"body"`
@@ -893,6 +914,11 @@ func (cli *githubClient) updateIssueBody(number int, body string) error {
 
 // addIssueComment adds a markdown comment to the numbered issue.
 func (cli *githubClient) addIssueComment(number int, comment string) error {
+	if cli.divertChanges {
+		cli.changes = append(cli.changes, addIssueComment{number, comment})
+		return nil
+	}
+
 	// https://docs.github.com/en/rest/issues/comments#create-an-issue-comment
 	var payload struct {
 		Body string `json:"body"`

gopls/internal/telemetry/cmd/stacks/stacks_test.go

@@ -7,6 +7,7 @@
 package main
 
 import (
+	"strings"
 	"testing"
 )
 
@@ -128,8 +129,54 @@ func TestParsePredicateError(t *testing.T) {
 	} {
 		if _, err := parsePredicate(expr); err == nil {
 			t.Errorf("%s: got nil, want error", expr)
-		} else {
-			t.Logf("%s: %v", expr, err)
 		}
 	}
 }
+
+// which takes the bulk of the time.
+func TestUpdateIssues(t *testing.T) {
+	if testing.Short() {
+		t.Skip("downloads source from the internet, skipping in -short")
+	}
+	c := &githubClient{divertChanges: true}
+	issues := []*Issue{{Number: 1, newStacks: []string{"stack1"}}}
+	info := Info{
+		Program:        "golang.org/x/tools/gopls",
+		ProgramVersion: "v0.16.1",
+	}
+	const stack1 = "stack1"
+	id1 := stackID(stack1)
+	stacks := map[string]map[Info]int64{stack1: map[Info]int64{info: 3}}
+	stacksToURL := map[string]string{stack1: "URL1"}
+	updateIssues(c, issues, stacks, stacksToURL)
+
+	if g, w := len(c.changes), 2; g != w {
+		t.Fatalf("got %d changes, want %d", g, w)
+	}
+	// The first change creates an issue comment.
+	cic, ok := c.changes[0].(addIssueComment)
+	if !ok {
+		t.Fatalf("got %T, want addIssueComment", c.changes[0])
+	}
+	if cic.number != 1 {
+		t.Errorf("issue number: got %d, want 1", cic.number)
+	}
+	for _, want := range []string{"URL1", stack1, id1, "golang.org/x/tools/[email protected]"} {
+		if !strings.Contains(cic.comment, want) {
+			t.Errorf("missing %q in comment:\n%s", want, cic.comment)
+		}
+	}
+
+	// The second change updates the issue body.
+	ui, ok := c.changes[1].(updateIssueBody)
+	if !ok {
+		t.Fatalf("got %T, want updateIssueBody", c.changes[1])
+	}
+	if ui.number != 1 {
+		t.Errorf("issue number: got %d, want 1", cic.number)
+	}
+	want := "Dups: " + id1
+	if !strings.Contains(ui.body, want) {
+		t.Errorf("missing %q in body %q", want, ui.body)
+	}
+}