gopls/internal/test/integration: fix race in TestGCDetails_Toggle

The AfterChange predicate is insufficient for awaiting the GC details
command. We must await the specific diagnosis of GC details.

Fix the predicate, and update the documentation for AfterChange to more
clearly spell out what it awaits.

Fixes golang/go#67428

Change-Id: I4923a4dac773f2c953a21bf026cadca4b9370ef3
Reviewed-on: https://go-review.googlesource.com/c/tools/+/586878
Reviewed-by: Alan Donovan <[email protected]>
Auto-Submit: Robert Findley <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: findleyr

gopls/internal/test/integration/codelens/gcdetails_test.go

@@ -49,11 +49,14 @@ func main() {
 		env.OpenFile("main.go")
 		env.ExecuteCodeLensCommand("main.go", command.GCDetails, nil)
 
-		env.AfterChange(Diagnostics(
-			ForFile("main.go"),
-			WithMessage("42 escapes"),
-			WithSeverityTags("optimizer details", protocol.SeverityInformation, nil),
-		))
+		env.OnceMet(
+			CompletedWork(server.DiagnosticWorkTitle(server.FromToggleGCDetails), 1, true),
+			Diagnostics(
+				ForFile("main.go"),
+				WithMessage("42 escapes"),
+				WithSeverityTags("optimizer details", protocol.SeverityInformation, nil),
+			),
+		)
 
 		// GCDetails diagnostics should be reported even on unsaved
 		// edited buffers, thanks to the magic of overlays.

gopls/internal/test/integration/expectation.go

@@ -342,9 +342,14 @@ func (e *Env) DoneDiagnosingChanges() Expectation {
 
 // AfterChange expects that the given expectations will be met after all
 // state-changing notifications have been processed by the server.
-//
-// It awaits the completion of all anticipated work before checking the given
-// expectations.
+// Specifically, it awaits the awaits completion of the process of diagnosis
+// after the following notifications, before checking the given expectations:
+//   - textDocument/didOpen
+//   - textDocument/didChange
+//   - textDocument/didSave
+//   - textDocument/didClose
+//   - workspace/didChangeWatchedFiles
+//   - workspace/didChangeConfiguration
 func (e *Env) AfterChange(expectations ...Expectation) {
 	e.T.Helper()
 	e.OnceMet(