From 3b49124c9f463821bdcd25989a827f6660bacb22 Mon Sep 17 00:00:00 2001
From: Adam Luzsi <adamluzsi@gmail.com>
Date: Tue, 5 Mar 2024 20:48:20 +0100
Subject: [PATCH] clock pkg optimisation

---
 clock/Clock.go      | 6 +++++-
 clock/Clock_test.go | 8 ++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/clock/Clock.go b/clock/Clock.go
index 4c9ed54..e122ff5 100644
--- a/clock/Clock.go
+++ b/clock/Clock.go
@@ -15,8 +15,12 @@ func Sleep(d time.Duration) {
 }
 
 func After(d time.Duration) <-chan time.Time {
-	startedAt := internal.GetTime()
 	ch := make(chan time.Time)
+	if d == 0 {
+		close(ch)
+		return ch
+	}
+	startedAt := internal.GetTime()
 	go func() {
 	wait:
 		for {
diff --git a/clock/Clock_test.go b/clock/Clock_test.go
index 74541a1..ca8542d 100644
--- a/clock/Clock_test.go
+++ b/clock/Clock_test.go
@@ -220,6 +220,14 @@ func TestAfter(t *testing.T) {
 			t.Fatal("clock.After should have finished already its work after travel that went more forward as the duration")
 		}
 	}) //Ω, testcase.Flaky(5*time.Second))
+
+	s.Test("no matter what, when the wait time is zero, clock.After returns instantly", func(t *testcase.T) {
+		timecop.SetSpeed(t, 0.001)
+		timecop.Travel(t, time.Second, timecop.Freeze())
+		assert.Within(t, time.Millisecond, func(ctx context.Context) {
+			<-clock.After(0)
+		}, "expected to finish instantly")
+	})
 }
 
 func Test_testTimeWithMinusDuration(t *testing.T) {