gopls/internal/regtest: await go.work changes in TestAddAndRemoveGoWork

To temporarily avoid flakes, wait for go.work changes to be processed
before reopening files. This merely works around the underlying bug, as
noted in the comment.

For golang/go#57508

Change-Id: I80d24c16ff709ff77a0fb07dd3ac7275bc8bcb5a
Reviewed-on: https://go-review.googlesource.com/c/tools/+/459784
Auto-Submit: Robert Findley <[email protected]>
gopls-CI: kokoro <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Robert Findley <[email protected]>
Reviewed-by: Alan Donovan <[email protected]>

Author: findleyr

gopls/internal/regtest/workspace/workspace_test.go

@@ -1134,6 +1134,14 @@ use (
 		// Removing the go.work file should put us back where we started.
 		env.RemoveWorkspaceFile("go.work")
 
+		// TODO(golang/go#57508): because file watching is asynchronous, we must
+		// ensure that the go.work change is seen before other changes, in order
+		// for the snapshot to "know" about the orphaned b/main.go below.
+		//
+		// This is a bug, plain and simple, but we await here to avoid test flakes
+		// while the underlying cause is fixed.
+		env.Await(env.DoneWithChangeWatchedFiles())
+
 		// TODO(rfindley): fix this bug: reopening b/main.go is necessary here
 		// because we no longer "see" the file in any view.
 		env.CloseBuffer("b/main.go")