diff --git a/internal/lsp/regtest/diagnostics_test.go b/internal/lsp/regtest/diagnostics_test.go
index 8a46bf9008..11c893192b 100644
--- a/internal/lsp/regtest/diagnostics_test.go
+++ b/internal/lsp/regtest/diagnostics_test.go
@@ -28,13 +28,21 @@ func main() {
 }`
 
 func TestDiagnosticErrorInEditedFile(t *testing.T) {
+	// This test is very basic: start with a clean Go program, make an error, and
+	// get a diagnostic for that error. However, it also demonstrates how to
+	// combine Expectations to await more complex state in the editor.
 	runner.Run(t, exampleProgram, func(t *testing.T, env *Env) {
 		// Deleting the 'n' at the end of Println should generate a single error
 		// diagnostic.
 		env.OpenFile("main.go")
 		env.RegexpReplace("main.go", "Printl(n)", "")
 		env.Await(
-			env.DiagnosticAtRegexp("main.go", "Printl"),
+			// Once we have gotten diagnostics for the change above, we should
+			// satisfy the DiagnosticAtRegexp assertion.
+			OnceMet(
+				CompletedWork(lsp.DiagnosticWorkTitle(lsp.FromDidChange), 1),
+				env.DiagnosticAtRegexp("main.go", "Printl"),
+			),
 			// Assert that this test has sent no error logs to the client. This is not
 			// strictly necessary for testing this regression, but is included here
 			// as an example of using the NoErrorLogs() expectation. Feel free to
diff --git a/internal/lsp/regtest/env.go b/internal/lsp/regtest/env.go
index 1865b80472..30ab143cf8 100644
--- a/internal/lsp/regtest/env.go
+++ b/internal/lsp/regtest/env.go
@@ -259,6 +259,29 @@ const (
 	Unmeetable
 )
 
+// OnceMet returns an Expectation that, once the precondition is met, asserts
+// that mustMeet is met.
+func OnceMet(precondition Expectation, mustMeet Expectation) *SimpleExpectation {
+	check := func(s State) (Verdict, interface{}) {
+		switch pre, _ := precondition.Check(s); pre {
+		case Unmeetable:
+			return Unmeetable, nil
+		case Met:
+			verdict, metBy := mustMeet.Check(s)
+			if verdict != Met {
+				return Unmeetable, metBy
+			}
+			return Met, metBy
+		default:
+			return Unmet, nil
+		}
+	}
+	return &SimpleExpectation{
+		check:       check,
+		description: fmt.Sprintf("once %q is met, must have %q", precondition.Description(), mustMeet.Description()),
+	}
+}
+
 func (v Verdict) String() string {
 	switch v {
 	case Met: