gopls/internal/cmd/help_test.go: document

Change-Id: Ia1d242e67fe36d5042891ee2db69a01b092d6b84
Reviewed-on: https://go-review.googlesource.com/c/tools/+/544256
Auto-Submit: Alan Donovan <adonovan@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

gopls/internal/cmd/help_test.go

@@ -4,6 +4,14 @@
 
 package cmd_test
 
+// This file defines tests to ensure the cmd/usage/*.hlp files match
+// the output of the tool. The .hlp files are not actually needed by
+// the executable (they are not //go:embed-ded, say), but they make it
+// easier to review changes to the gopls command's help logic since
+// any effects are manifest as changes to these files.
+
+//go:generate go test -run Help -update-help-files
+
 import (
 	"bytes"
 	"context"
@@ -18,8 +26,6 @@ import (
 	"golang.org/x/tools/internal/tool"
 )
 
-//go:generate go test -run Help -update-help-files
-
 var updateHelpFiles = flag.Bool("update-help-files", false, "Write out the help files instead of checking them")
 
 const appName = "gopls"